Tow/Haul button......and Auto 4wd

daevans315 · Post by **daevans315** » Tue Jul 25, 2006 9:46 am

I have confidence now that eventually this is going to work. I don't think the correct change had ever been made on the PCM. Now I want to get the light on the dash to work. It seems that a few people on this board have had more electronics background that I have so please correct me. But here is what I'm thinking...

Take the Latched On/Off Output Using a Single Momentary Pulse circuit from here. http://www.the12volt.com/relays/page5.asp#lsp . Spice the output into the wire to the tow haul light. The momentary ground will come from the same switch as the PCM. I think this circuit board is a good cheep solution to getting all the relays in a small package. http://www.amazon.com/gp/product/tech-d ... 06?ie=UTF8

The amperage draw is WAY overboard for these relays but its $9 so who cares.

Has anybody had the dash apart to know if there is actually a bulb in the tow haul socket?????

crew cab sonoma · Post by **crew cab sonoma** » Wed Aug 02, 2006 4:45 am

just a guess, but figuring since none of the S-series trucks ever got the tow/haul feature, i`d be willing to bet GM elected not to spend the extra $.03 per cluster to install this bulb...

2kwik4u · Post by **2kwik4u** » Wed Aug 02, 2006 6:13 am

crew cab sonoma wrote:just a guess, but figuring since none of the S-series trucks ever got the tow/haul feature, i`d be willing to bet GM elected not to spend the extra $.03 per cluster to install this bulb...

Some of the S-series did get it though. My dads Envoy has it, as well as Steve's Jimmy Diamond Edition had it.

It's there, just a matter of figuring out HTF to get it to work properly.

I know they spent the extra $0.03 to run the wires for a Tach in my Xtreme. I didn't come with one, but has one now, and all I did was plug in the new cluster. Ultimately it's cheaper to make one harness, than it is to make two different ones.

daevans315 · Post by **daevans315** » Thu Aug 03, 2006 6:58 am

Update: Bryan and I are still working on this. It turns out that he is using ls1 edit, which does not have the 'button' to change the pcm from looking at the bcm to looking at Pin 71. The LS1 Edit guys are not giving him much hope that they ever will support this feature. He does, however, have access to efi Live and after my vacation (the one I hoped to have this done before) I will be sending off my PCM one more time to have it flashed with the the new correct tow haul switch setting.

I have to say that even though this has been lengthy, Bryan at pcmforless.COM has stuck with me all the way through this. Every email I've sent him has been returned the next business day(sometimes within hours or mins). He has made a honest effort to make this right and I will have had his 'loaner' PCM for over 2 months by the time this all gets settled.
I would not hesitate to recommend him for future PCM work.

2kwik4u · Post by **2kwik4u** » Thu Aug 03, 2006 7:05 am

daevans315 wrote:Update: Bryan and I are still working on this. It turns out that he is using ls1 edit, which does not have the 'button' to change the pcm from looking at the bcm to looking at Pin 71. The LS1 Edit guys are not giving him much hope that they ever will support this feature. He does, however, have access to efi Live and after my vacation (the one I hoped to have this done before) I will be sending off my PCM one more time to have it flashed with the the new correct tow haul switch setting.

I have to say that even though this has been lengthy, Bryan at pcmforless.COM has stuck with me all the way through this. Every email I've sent him has been returned the next business day(sometimes within hours or mins). He has made a honest effort to make this right and I will have had his 'loaner' PCM for over 2 months by the time this all gets settled.
I would not hesitate to recommend him for future PCM work.

Glad to hear that he's being such a good sport about all this. I have to think it's in his best interest in the long run as well, as this is a possible service that he can offer to others, as well as the word of mouth support he is getting from you. I have to say I have NEVER heard a bad word about him or that business at all. They must be doing something right.

I'm VERY VERY interested to see the outcome of all this, once the dust settles. Much thanks to both you and Bryan for the diligence on this one!

crew cab sonoma · Post by **crew cab sonoma** » Tue Aug 15, 2006 5:51 am

2kwik4u wrote: Some of the S-series did get it though. My dads Envoy has it, as well as Steve's Jimmy Diamond Edition had it.

It's there, just a matter of figuring out HTF to get it to work properly.

I know they spent the extra $0.03 to run the wires for a Tach in my Xtreme. I didn't come with one, but has one now, and all I did was plug in the new cluster. Ultimately it's cheaper to make one harness, than it is to make two different ones.

oh, my mistake. i didnt notice that some of the Blazer/jimmy/Bravadas got it, just none of the pickups.
perhaps you may have to get a PCM and BCM form one of those to make it work. who knows about the wiring harness...

crew cab sonoma · Post by **crew cab sonoma** » Tue Aug 15, 2006 8:15 am

also, did the Jimmys ect. that got tow/haul, all have floor shifter, or did some have the button on the column shifter as well?

daevans315 · Post by **daevans315** » Tue Aug 22, 2006 8:17 am

Well back from a 2 week, 1,500 mile trip with the crew, all towing a 3,000 pound trailer(the reason I wanted this silly button) but the crew did very well. I pulled the PCM last night and put it in the mail. We should have a final answer in less than a week.

daevans315 · Post by **daevans315** » Thu Aug 31, 2006 3:53 pm

IT WORKS!!!

Got the PCM back today and installed it. Touched the wire to ground and took it for a drive. There was a definite change in the shift points and shift firmness.

Now for the bad news.....
Its not nearly as ?aggressive? of a change as other vehicles I've driven with this feature. The average RPM’s I could get it to shift under light throttle and light load was about 2,500 RPM's 1-2 and 2-3. The others were at 3,000 to 3,500 under light loads. It does shift much quicker and firmer between the gears. There is little or no change in the down shift. Both my Dads Tahoe and the U-haul I drove in tow haul would drop back down a gear very early for engine braking. They would come into 2nd and 1st at about 3,000 RPM. I did not notice this on the crew. I may look into what it takes to make this happen on the shift tables and see about having them updated further. I also want to throw the trailer behind it and see how it does. The others may have been more aggressive as average trailer and load behind a Tahoe or U-haul weights far more than the average s-10 trailer.

But it does work.

Oh ya. No indicator light as expected.

2kwik4u · Post by **2kwik4u** » Fri Sep 01, 2006 2:36 am

Glad to hear that you got it setup, and working.

The downshift tables are similar to standard while in Tow/Haul mode (I think I posted screenshots somewhere).

Also the TCC lockup tables are more aggressive, and I can only assume that is why it feels as if it's shifting sooner.

Steventruck · Post by **Steventruck** » Thu Sep 14, 2006 12:48 pm

in regards to the clusters and light bulbs...

My truck, a 99 ZR2 reg cab pick up with manual tranny has a CHECK 4WD light. and all of the lights are LEDs and are there (except hi beam and turn indicators are regular lights). I think the CHECK 4WD is only used on the auto 4WD equiped models.

Steve

crew cab sonoma · Post by **crew cab sonoma** » Wed Sep 27, 2006 9:00 am

about the "AUTO 4WD" part of this thread...

not to be confusing "AUTO 4WD" with "All Wheel Drive" (AWD).
it appeasrs that S-series trucks/Blazers came with at least 3 different types of 4WD drive setups...

1: the std. push button 4WD system, found in most.

2: the "auto 4WD" push button systems found in some Blazers/Jimmys.

3: the All Wheel Drive full time 4WD (no push buttons) system, used in the Olds Bravadas.
now the Bravada setup (also similar to the Syclone/Typhoon and Astros) have a full time, single speed, Borg Warner transfer case with a viscous clutch. and the front differential without the disengagement cable.

here is a 2000 Blazer (TrailBlazer) with the "AUTO 4WD" system...
note the extra "Auto" button on the 4WD dash control switch...

ebay

and here is a 2000 Bravada, with "AWD"....
note the lack of any push button controls at all...
also note the 120 MPH speedo. but no shifter indicator in the tach....

ebay

now i may be wrong, but i see no reason why the "auto" system couldnt use the same NP-233 tranfer case, and other mechanical components as the std. 4WD setups.

perhaps the only real differences are the extra dash button, wiring, and a more sophisticated TCCM??? maybe the BCM is involved too? perhaps some extra sensor inputs, like an extra speed sensor somewhere, maybe???

so, just how much is really different between the std. and "Auto" systems?
are the transfer cases really different???

EDIT: it looks like the Auto system has a provision for a neutral position. i guess that would rule out the NP-233C transfer case?

link't long urls-HJ

crew cab sonoma · Post by **crew cab sonoma** » Tue Oct 03, 2006 9:26 am

i did some reasearch on the autotrac system...
it only uses the NV246 transfer case? is that right?

crew cab sonoma · Post by **crew cab sonoma** » Fri Dec 15, 2006 5:02 am

another thought on the tow/haul issue...

i sometimes place my shifter in second gear, to prevent downshifting to first in certain low speed stop and go driving conditions, where the tranny would normally be making lots of up-down gear changes.

with the TB mod, i often find the 2nd gear takeoffs to be much smoother, and actually preferable.

could the PCM be reprogramed to default to second gear launches under "normal" light throttle conditions, but resort to normal 1st gear operation when tow/haul mode is activated?

shift220 · Post by **shift220** » Fri Dec 22, 2006 9:48 am

I've been doing some research myself to figure out how to enter tow/haul mode with my truck (2wd 01 4.3L Noma). I have HPtuners to tune my truck and found out that inside the software you need to set how the mode is turned on. Stock it looks for the class 2 signal from the BCM. I also have the option to select "One Switch" and "Two Switches". One Switch is for grounding of pin 71 on the blue and should enable the mode. Two Switch is the grounding of two different pins, but i'm not sure of the difference.

Although I haven't had the chance to try this out yet because my truck isn't driveable, when I get the chance I will let you guys know.

2kwik4u · Post by **2kwik4u** » Fri Dec 22, 2006 10:24 am

crew cab sonoma wrote:another thought on the tow/haul issue...

i sometimes place my shifter in second gear, to prevent downshifting to first in certain low speed stop and go driving conditions, where the tranny would normally be making lots of up-down gear changes.

with the TB mod, i often find the 2nd gear takeoffs to be much smoother, and actually preferable.

could the PCM be reprogramed to default to second gear launches under "normal" light throttle conditions, but resort to normal 1st gear operation when tow/haul mode is activated?

You can modify the tables to do this, but I'm not sure how the trans would like it. That will create a bit more heat I would think.

Basically set all the shift tables up so that at 0mph, and 0%tps it would shift to second....Leave the tow/haul tables intact, and they will still work as intended.

My only concern is that the 1st and 2nd gear solenoids might end up fighting each other, and cause mecahnical problems......A trans expert will be needed to shed some more light on this.

crew cab sonoma · Post by **crew cab sonoma** » Fri Dec 22, 2006 12:04 pm

the tq. converter does stall a little higher from a dead stop, but once the truck is moving for a couple of seconds, it feels normal again. i would say that any increase in trans temps would be minimal.

i`ve done regularly with my CC, and my current truck, and have had no issues from it. dont forsee any, either.

as long as the tables were set up correctly, there shouldnt be an issue with the solenoids, but i dunno.

daevans315 · Post by **daevans315** » Mon Jun 18, 2007 9:32 am

I had not done much towing in the last 6 months so I didn't have any real updates, however, last week I picked up a 5 x 10 enclosed trailer. This weekend I loaded it down pretty heavy and drove 100 miles or so.
I like the shift pattern with a good heavy load in Tow mode. It holds each gear quite a bit longer and is defiantly firm and quick between shifts.
I still haven't hooked up a light yet. I'm not sure I am going to go to the trouble now. I mounted the switch under the dash by the E-brake release.
If I had it to do over again am not sure I would go to all the work I went through to install this mod. However, if I was spending the $$$ to have the PCM flashed I would turn this option on for sure.

2kwik4u · Post by **2kwik4u** » Mon Jun 18, 2007 9:34 am

daevans315 wrote:I had not done much towing in the last 6 months so I didn't have any real updates, however, last week I picked up a 5 x 10 enclosed trailer. This weekend I loaded it down pretty heavy and drove 100 miles or so.
I like the shift pattern with a good heavy load in Tow mode. It holds each gear quite a bit longer and is defiantly firm and quick between shifts.
I still haven't hooked up a light yet. I'm not sure I am going to go to the trouble now. I mounted the switch under the dash by the E-brake release.
If I had it to do over again am not sure I would go to all the work I went through to install this mod. However, if I was spending the $$$ to have the PCM flashed I would turn this option on for sure.

Good to hear. I've bought a boat since you went through all this, and have seriously been considering getting the PCM redone to include this, and eFan controls....We'll see if I ever get it done though.

crew cab sonoma · Post by **crew cab sonoma** » Mon Jul 16, 2007 5:16 am

2kwik4u wrote:
crew cab sonoma wrote:just a guess, but figuring since none of the S-series trucks ever got the tow/haul feature, i`d be willing to bet GM elected not to spend the extra $.03 per cluster to install this bulb...
Some of the S-series did get it though. My dads Envoy has it, as well as Steve's Jimmy Diamond Edition had it.

It's there, just a matter of figuring out HTF to get it to work properly.

I know they spent the extra $0.03 to run the wires for a Tach in my Xtreme. I didn't come with one, but has one now, and all I did was plug in the new cluster. Ultimately it's cheaper to make one harness, than it is to make two different ones.

just a follow up on this... i pulled my instrument cluster on my Extended Cab over the weekend, to disable that annoying airbag light, and noticed the "Tow/Haul" bulb (LED) was indeed installed on the circuit board...

2kwik4u · Post by **2kwik4u** » Mon Jul 16, 2007 6:15 am

I believe that the trucks were setup for it with everything BUT the shifter stalk with the button, and the appropriate program in the Body Control Module.

Sure would be nice if one of these companies like HPTuners or EFILive would learn to hack the BCM's as well!

crew cab sonoma · Post by **crew cab sonoma** » Mon Jul 16, 2007 6:36 am

just curious, of the blazers/Jimmys that had the ?Tow/Haul feature, did any have column shift, or were they all floor shifter equipped?

in other words, is there a column shifter asy. available for the S-series, that has the T/H button on it?

2kwik4u · Post by **2kwik4u** » Mon Jul 16, 2007 7:19 am

I'm not sure.....I can't say as I remember seeing one. My Dads Envoy has a button on the console I think.

daevans315 · Post by **daevans315** » Wed Nov 28, 2007 7:46 am

I was using my crew as a tractor over the holiday dragging a tandem dump trailer around a building site. I was in low 4 all day shuttling dirt around the 5 acer site. About half way through the day, I thought.. humm wonder what tow haul does in low range.... I'm towing right?

Don't do this in low range. The shifts where VERY harsh. You could see in my tracks where it started to spin every time it shifted from 1st to 2nd even with a loaded 8 or 9,000 pound trailer behind it. I don't know if the normal setup locks out tow haul mode in 4 low but I won't be doing it again myself.

2kwik4u · Post by **2kwik4u** » Fri Nov 30, 2007 9:47 am

Just saw this picture on another site and thought it would fit well in this thread. Notice the grey button just behind and to the left of the shifter on the console. Thats the tow haul button as installed in some S-series trucks.

You can also see that this particular truck has the Autotrac transfer case, and Auto 4wd setting.

Sure wish they would've had both of those items in my ZR5. I probably would've still had the truck

drperry · Post by **drperry** » Thu Jan 10, 2008 2:53 pm

crew cab sonoma wrote:3: the All Wheel Drive full time 4WD (no push buttons) system, used in the Olds Bravadas.
now the Bravada setup (also similar to the Syclone/Typhoon and Astros) have a full time, single speed, Borg Warner transfer case with a viscous clutch. and the front differential without the disengagement cable.

There's at least one Blazer on BlazerForum (can't remember the user name) that's got AWD...

So it must've been one of those hidden options...

And I have seen Blazers' with the tow/haul switch on the end of the column shifter...

Torskdoc · Post by **Torskdoc** » Fri Jan 11, 2008 2:14 pm

Would taking a BCM out of a junked Blazer with Tow/Haul work. I read somewhere that the CC got the wiring harness that the Ute's got. This MAY be the way to go (ease of changeover) provided all else is equal (accessories, year, etc.)

Larry

drperry · Post by **drperry** » Fri Jan 11, 2008 3:03 pm

You'd need the PCM too... The whole VIN security and communications thing...

crew cab sonoma · Post by **crew cab sonoma** » Sun Apr 27, 2008 1:30 pm

drperry wrote:
crew cab sonoma wrote:3: the All Wheel Drive full time 4WD (no push buttons) system, used in the Olds Bravadas.
now the Bravada setup (also similar to the Syclone/Typhoon and Astros) have a full time, single speed, Borg Warner transfer case with a viscous clutch. and the front differential without the disengagement cable.

There's at least one Blazer on BlazerForum (can't remember the user name) that's got AWD...

So it must've been one of those hidden options...

And I have seen Blazers' with the tow/haul switch on the end of the column shifter...

thanks for that info. i think i have seen that AWD Blazer too... a 96 or 97 model, i think?

crew cab sonoma · Post by **crew cab sonoma** » Sun Apr 27, 2008 1:47 pm

drperry wrote:You'd need the PCM too... The whole VIN security and communications thing...

just out of curiosity, i completely unplugged my BCM on my 2000 truck, and it started and ran without it... the essential systems seemed to work ok, all the gauges worked, shifter indicator, heat/vent controls responded normally, headlights worked when switched manually. radio worked (non RDS).

the "security" light was lit, and the fog lights wouldnt turn on, and the keyless entry woudnt work, but the power locks still functioned with the door switches, but otherwise the truck functioned normally...

perhaps the "VIN security" issue only applies to later models?
if so, what year? 01-later, or perhaps 02, or 03?

crew cab sonoma · Post by **crew cab sonoma** » Thu May 01, 2008 3:59 am

also, my odometer was still reading correctly too.

Steventruck · Post by **Steventruck** » Wed Jan 14, 2009 7:05 am

Back to the original question, My wife's 2000 ZR2 Blazer has the tow/haul mode already programmed into it.

To be clear, this Blazer did NOT have it as an option. I was swapping the good battery from her Blazer in the her Impala SS which had a discharged RedTop Optima so she could get to work. So then I had a mostly dead Optima in the blazer. When I jumped it off of my truck, Her Blazer started, but the tow/haul light came on. I drove it like that for about 25 miles and it was definately a different shift pattern. When I got to where I was going, I turned off the truck, then re-started it and it behaved like normal.

Hmmm.

So later in the week, I went to the local junkyard and picked up a switch and the entire wiring for the center console of a T/H equipped blazer. the switch has three wires. On the plugs into an empty spot on one of the BCM connectors, one to ground, and one to the dimmable interior (instrument Panel) lights (grey wire).

The wiring section actually has 7 or 8 wires in it. Three for the T/H switch, plus an instrument panel light (dimmable backlight for the floorshift gear indicator) and something else (i forget). I also grabbed the vehicle end of the plug from the donor vehicle and traced the 18" or so of wiring to the BCM so I released that pin from the BCM wiring harness. This made the switch plug-n-play, I just had to tap into a ground and back-lighting (I/P circuit), then find a mounting spot for the switch.

I hooked it up and it works perfectly... with no reprogramming!

Steve

Picture

Post by **HenryJ** » Wed Jan 14, 2009 7:21 am

Good to hear. Do you suppose that switch just grounds a pin in the BCM momentarily? That would make an easy install for any momentary switch.

Now to try this on a crew cab

Do we have the tow/haul light?

I don't recall seeing it. RATS! That is not going to work.

Steventruck · Post by **Steventruck** » Wed Jan 14, 2009 7:37 am

All of the S10 clusters are the same. You do have the tow/haul light in your cluster. If you take a really bright flashlight and shine it at your cluster, you should see it. It will be on the left side at the top, next to the SHIFT light (which also probably doesn't operate on the crewcabs).

I tried putting a cluster from a column-shift blazer into my mom's Bravada (floor-shift) and the gear indiator on the cluster worked! I thought it was really cool, but my mom prefers the easier-to-read Bravada cluster.

So many of these parts are interchangeble.

And yes, the switch is momenary contact.

Steve

Post by **HenryJ** » Wed Jan 14, 2009 11:36 am

Ok, I see that you are correct and the crew cab does have the Tow/Haul indicator in the instrument cluster. Just left of center.

So if I gather this correctly, you got the switch with wires. Installed one wire into your BCM connector and the other two needed for the switch and you now have the tow/haul working?

Any chance of letting us see which wire you added to the BCM connector? Color and position would be helpful. A picture would be great.

Sounds like this might be worth a try.

Post by **HenryJ** » Wed Jan 14, 2009 1:52 pm

Ok, don't kill yourself getting pictures.

I too made a run to the local salvage yard. I found a 1999 Jimmy that has the tow /haul switch. It was mounted in the center shift console. The wiring goes forward to a connector at the firewall near the BCM. One light blue wire goes to the brown BCM connector, in position B12.

I will be separating the harness to eliminate the wiring for the floor shift and see what else needs to be done to ease the install. I should know soon if this works for a crew cab.

green02crew · Post by **green02crew** » Wed Jan 14, 2009 2:57 pm

I would be very interested in a good write up. I have wanted this feature for some time now. If it is as simple as a switch and wire, even better.

Post by **HenryJ** » Wed Jan 14, 2009 5:09 pm

It looks like it may just be that simple. Everything posted makes sense to me, and that can be difficult sometimes

Describing the process of gathering the wiring is going to be difficult to convey. Our harness does not have the needed connector to make it truly "plug-n-play". The donor harness does include the correct terminal, which will make things simpler.

I like the dash install location, as our rear wiper/hatch switch connectors have the needed dash light and ground wires. Those with the blank panel will find it easy to install the Tow/Haul switch in this panel. I have installed a switch there, so I will likely install the switch in the dash as pictured above.

green02crew · Post by **green02crew** » Wed Jan 14, 2009 6:18 pm

I will have to find an alternative switch. I already know that the yards around here won't have one. That rules out the wiring harness for me as well.

Post by **HenryJ** » Wed Jan 14, 2009 8:47 pm

Good news and bad.

First the good. If you carefully separate the wiring and free the three terminals from the harness, you will have what you need to install with no cutting or splicing.
I was wrong. The connector we need is indeed there stuffed up behind the heater duct at the firewall. It has a male connector with one wire pair looped/jumpered. This has all the needed wiring to the BCM as well as your ground and dash lights wire.
Unplug this connector and you add the three wires from the Tow/Haul switch. The terminals slide right into place. Black to one side, gray in the middle and blue to the other side.
The switch does indeed momentarily ground the blue wire that goes to the BCM. The switch is 1" square. Pretty easy to drill holes for the corners and connect the dots to mount the switch.
Once installed the light works with the lights just like it should.

The bad news.
It did not work. The Tow/Haul light on the dash does not illuminate.
I can only guess that a different BCM may be needed. I have not heard that the BCM can be flashed. If that is possible, then that might be an option. I wonder if the BCM from my donor Jimmy might work?

I did take pictures, but they are useless until this works. Maybe someday we will figure this out.

green02crew · Post by **green02crew** » Wed Jan 14, 2009 11:18 pm

So close yet so far.

04crewvt · Post by **04crewvt** » Thu Jan 15, 2009 4:59 am

This might be obvious but overlooked. Did you unhook the battery and then reconnect it when you worked on the wiring? If not maybe the BCM needs a reboot to see the new circuit?

Post by **HenryJ** » Thu Jan 15, 2009 7:15 am

I have a battery disconnect switch. It is easy to disconnect the battery. I did work with the battery off.

04crewvt · Post by **04crewvt** » Thu Jan 15, 2009 7:47 am

Dang, it was worth a shot.

Steventruck · Post by **Steventruck** » Thu Jan 15, 2009 10:48 am

You could try swaping in the BCM from the donor vehicle. I had forgotten that I had previously swapped BCMs so she could have factory fog lights. I believe, however, that the shift tables and stuff are in the PCM.

A BCM swap is plug-n-play. The biggest thing is that you will have to get it to recognize your key. This process takes about 20 minutes.

after BCM swap is complete, attempt to start truck, it won't start and the the security light will flash.
leave the key in the on position with the security light flashing. You might want to set fan speed to off to save on your battery, but not nessesary.
after ten or so minutes, the security light will go out.
turn key off
restart truck, it should work

If that didn't work, try skipping the turn key off step, I can't quite remember right now.

I wonder what would happen if I did this mod on my truck (manual trans), My BCM is out of a blazer (with fog lights and computerized climate control)

Steve

Post by **HenryJ** » Thu Jan 15, 2009 11:04 am

Seems like you are in for a mess by doing this BCM swap. What happens to my factory fogs, trip computer, heated mirros, security, etc? This BCM might not have everything my truck has.

Steventruck · Post by **Steventruck** » Thu Jan 15, 2009 12:20 pm

In a mess? My truck work just fine. So does my wife's Blazer.

I was only suggesting that you could try a different BCM. The Security feature I have already discussed. If the tow/haul mode doesn't work after the swap, or you lose any of your stock features, then swap back.

When I swapped BCMs in my ZR2 pickup with Manual trans, 3.73 gears, 31" tires, no DRLs, and no fog lights for one that was from a 4 door blazer with auto trans, 3.42 gears, 235/75 tires, with DRLS, fogs, and CCC, I performed the swap, but carried my stock BCM in the glovebox in case a problem arose. I never went back.

Steve

Post by **HenryJ** » Mon Jan 19, 2009 2:59 pm

I have some unexpected time to kill for a while , so I decided to pursue this further. I went back to the salvage yard and grabbed the BCM from that Jimmy. It turns out it was a 2000 model year four door GMC Jimmy (S15) I checked and it did have factory fogs as well as the Tow/Haul. I figured I would give it a shot. I have $25 invested in the BCM , wiring and switch.
Once installed it did not start as expected. Having been prewarned, I expected that. I left the key on and waited ten minutes. Trying again it did not start. Hmmm. In for some more research while the key is on another ten minutes...

excerpts from GM data wrote:The passlock system uses a lockout cycle in order to synchronize all of the passlock components when any passlock related part is changed. The passlock system requires 3 consecutive lockout cycles in order to complete the 30 minute learn procedure for the changed component.

Changing the passlock components:
The design of the passlock system is to prevent theft even if various theft deterrent parts are changed.
The parts that can not be changed without going into the tamper mode are: The passlock sensor, BCM and VCM/PCM.
If any of these parts are replaced the vehicle may start and stall for 10 minutes. This is the long tamper mode. If this occurs, the system must go through a long tamper mode cycle. During this time the security telltale will be flashing for the full ten minutes and the DTC B3031 will be set. The BCM and the PCM require a full ten minutes in order to complete a learn cycle. The ignition switch must remain in the RUN position until the security telltale stops flashing. You need to repeat the cycle if the ignition switch does not remain in the RUN position.

Programming the theft deterrent system components:

30 minute learn procedure:
1. Turn ON the ignition, with the engine OFF
2. Attempt to start the engine, then release the key to ON (vehicle will not start)
3. Observe the SECURITY telltale, after approximately ten minutes the telltale will turn off.
4. Turn off the ignition and wait 5 seconds
5. Repeat steps 1-4 two more times for a total of three consecutive cycles/30 minutes (the vehicle is now ready to relearn the passlock sensor data code and/or passwords on the next ignition switch transition from OFF to CRANK)

So now I wait for the third cycle of ten minute waits to complete. I shut the key off and try starting. Same thing. It dies , but now the security light is not flashing. I guess that is progress. I try a second and third time to start it. Finally it starts! Push the TOW/Haul button and the dash light illuminates. Seems to run OK, so I shut it down, kill the battery and put it all back together.

I have not driven it yet, but I do have a button that lights up a Tow/Haul on the dash. My fog lights still work as the should and the truck runs.
I took pictures along the way and will get a write up together soon if indeed this is now working as it should.

04crewvt · Post by **04crewvt** » Mon Jan 19, 2009 3:04 pm

This sounds great! Can't wait to see your impressions of how well it works.

F9K9 · Post by **F9K9** » Mon Jan 19, 2009 5:10 pm

Stop it! Please, stop it! I know you can't but, I thought that a little whimpering might help.

I was over halfway to Ontario when we met, I might as well complete the trek to catch up on a few mods!

Post by **HenryJ** » Mon Jan 19, 2009 6:13 pm

You are welcome any time!

This may be premature, as it is untested, but here it is: Tow / Haul Mod

green02crew · Post by **green02crew** » Mon Jan 19, 2009 6:17 pm

Are the shift points changed?

04crewvt · Post by **04crewvt** » Mon Jan 19, 2009 7:06 pm

Now I will have to see if I have the light in the 2004 dash since they deleted so many other things, with my luck they were out of that wire harness and dash cluster.

Post by **HenryJ** » Mon Jan 19, 2009 7:29 pm

green02crew wrote:Are the shift points changed?

Yes. They are higher, firmer and it does not shift to OD.

GM Owners manual wrote:Tow/Haul Mode (V6 Engine, Automatic Transmission Equipped Models) (If Equipped)

The Tow/Haul Mode is a feature that assists when pulling a heavy trailer. The purpose of the Tow/Haul Mode is:

Reduce the frequency of shifts when pulling a heavy trailer.
Provide the same shift feel when pulling a heavy trailer as when the vehicle is unloaded.
Reduce the need to change throttle position when pulling a heavy trailer.

This feature is turned on or off by pressing a button on the floor console. When the feature is on, a light on the instrument panel will illuminate to indicate that the Tow/Haul Mode has been selected.

The Tow/Haul Mode is automatically turned off each time the vehicle is started.
The Tow/Haul Mode is most effective when the vehicle and trailer combined weight is at least 75% of the Gross Vehicle Weight Rating (GVWR) and the maximum trailer weight rating for the vehicle.

The Tow/Haul Mode for hauling a heavy trailer is most useful under the following conditions

When driving through hilly terrain at speeds below 55 mph (88 km/h).
When driving in low speed or stop and go traffic below 55 mph (88 km/h).
When driving in parking lots.

Use the Tow/Haul Mode instead of the previous recommendation to shift to THIRD (3) gear to improve fuel economy at highway speeds and shift performance at lower speeds. Operating in the Tow/Haul Mode when not pulling a heavy trailer will not cause damage to the vehicle, but you may experience reduced fuel economy and undesirable performance from the engine and transmission. The Tow/Haul Mode should be used only when pulling a heavy trailer.

• Examples of altered shift speeds when in tow/haul:

- Minimum 1-2 shifts pushed out approximately 13 km/h (8 mph)

- Minimum 2-3 shifts pushed out approximately 24 km/h (15 mph)

- Minimum 3-4 shifts pushed out approximately 48 km/h (30 mph)

- Tow/haul only affects shift points below 88 km/h (55 mph).

Tested and working just fine. Thanks for the push Steventruck

Post by **HenryJ** » Mon Jan 19, 2009 8:27 pm

Via Jackson, Mike Copeland wrote:To your tow / haul question. Putting the trans in the tow mode does raise the line pressure, and the shift RPM. It raises the shift RPM by delaying the shift timing. This is to help eliminate repeated up and down shifts. Every time a trans shifts, or a converter engages, there is some slippage in the components. This slippage wears components, and builds heat. In a 4L70E (same as a 700R4, 4L60, 4L60E, and 4L65E) 2nd and 4th gear are engaged when a band inside the transmission stops a spinning drum. These shifts build more heat that the clutch apply for 3rd gear. To lock the converter, pressure is applied to a small clutch in the torque converter. This is a pretty small clutch, and cannot take a lot of abuse. That is one reason it is never engaged at WOT. The main goal of tow mode is to reduce the amount of heat generated, and the reduce as much wear of the components as possible. In the old days before computer controlled transmissions, there was no easy way to change shift points or line pressure.

This being said, the real purpose of the tow / haul mode is to eliminate wear and excessive heat in the trans. By raising the shift point, we delay the number of shifts. If the trans is held in a gear longer, it helps eliminate downshifting as often. There is more torque available because of the increased gear ratio and RPM. By increasing the line pressure, we apply increased force on the clutches and bands. This reduces the heat and wear when the trans shifts. By delaying the engagement of the lock-up converter, we increase the trans heat a little because of the shear of the trans fluid in the converter, but we eliminate the wear and heat generated by engaging and releasing the converter clutch.

Adding a aftermarket controller, like a Superchip, does the same basic thing to the non-tow engaged calibration. In most cases, the tow mode raises it even more, and people may not see converter engagement at all when towing a load. My truck has a Superchip, and my converter engagement is delayed a lot in tow mode.

green02crew · Post by **green02crew** » Tue Jan 20, 2009 5:39 am

Now to find the BCM , wiring and switch! Online locations anyone?

Steventruck · Post by **Steventruck** » Thu Jan 22, 2009 6:56 am

Glad I could help.

Steve

daevans315 · Post by **daevans315** » Fri Jan 23, 2009 12:18 pm

Man. I wish we had figured out the BCM \ VAT solution in 2006 when I set mine up. Oh well.. live and learn. Probably not worth all the changes to back mine out just to make the light come on on the dash.

Post by **HenryJ** » Fri Jan 23, 2009 12:34 pm

It is amazing how sometimes we wait and a simple solution presents itself. The steering wheel radio control was another one that reminds me of this.
This one was slightly more complex, but still pretty easy.

I have played with it a little here and there. The difference is very noticeable. It will be a huge help when heavily loaded, or when towing.

green02crew · Post by **green02crew** » Fri Jan 23, 2009 1:15 pm

I have made calls around here and cannot come up with a BCM let alone the wiring and button. The yards do not have anything available. I used the VIN that HJ had photoed in the glovebox for a search as well through the yards with no luck. Anybody know where I can secure a BCM with the needed features and wiring harness/button?

daevans315 · Post by **daevans315** » Fri Jan 23, 2009 1:20 pm

HenryJ wrote:.

I have played with it a little here and there. The difference is very noticeable. It will be a huge help when heavily loaded, or when towing.

I still use mine regularly. I just had it on for a trip our of down town chicago with a 6x12 U-haul trailer. It was invaluable for the downtown traffic but I probably won't do that again...

OT:
The trip really wasn't much fun. For those of you that don't know, Chicago's "subway" is called the 'L' for elevated train. The older parts of the subway runs on tracks elevated over the downtown streets with posts coming down between the lanes of traffic. So for many of the down streets you have a parking \ turn lane, posts that support the L, then 2 lanes of traffic (sometimes 1 way sometimes 2 way) then then a set of posts for the L then another parking \ turn lane. Of course where I was going was a condo building where one of the North South lines crosses the East West lines so there was no avoiding the L... It was interesting to say the least.. At least I didn't care about the trailer...

green02crew · Post by **green02crew** » Fri Jan 23, 2009 10:50 pm

I am still looking with no luck. I have read online that the BCM can be programmed and features added with a Tech2 scan tool. My local GM dealership informs me otherwise. I have searched for a BCM using the numbers available from the vehicle HenryJ scavenged with no luck. The numbers just don't appear to match up. I have come across some BCMs with the yellow block but am unsure that the yellow block denotes tow/haul.

If someone is near a yard with tow/haul equipped s-series and feels like yanking a BCM, switch and wire/button and feels like mailing one to me it would be appreciated!

I have attempted to contact s10warehouse on ebay for parts before that are not listed and they never got back to me so I don't see that as a viable option although I'm sure they have come across the necessary equipment before.

green02crew · Post by **green02crew** » Thu Feb 05, 2009 7:11 pm

Received BCM, attempting install in the AM if time permits.

Post by **HenryJ** » Thu Feb 05, 2009 7:45 pm

green02crew wrote:Received BCM, attempting install in the AM if time permits.

Woo Hoo!

Remember it may take nearly an hour just to relearn, once everything is installed.

green02crew · Post by **green02crew** » Fri Feb 06, 2009 9:45 am

Install was very straight forward.

Look at the photos that were posted carefully, I confused the black and blue wires on the harness behind the heater and wondered why the switch did not work. Switched the wires and all was fine. My harness was easily pulled out, I could see it sticking out from behind the heater and just pulled slightly and it was readily available.

Don't do the mod in the cold. I attempted to pull the plastic out of the way on the lower dash and it snapped. I screwed it back in and it looks ok but it is broken. Same goes for the clips holding the BCM in place, they broke in the cold as well. Was approximately 0*, maybe I just pulled too hard but they seemed brittle, could be age as well. Where the BCM is located the clips holding it in don't appear necessary since its location is so tight (atleast I'm hoping).

I went to do the relearn and my truck started right up first turn as if nothing had changed. The security light did flash and I did the relearn procedure which was successful (only taking about 20min) and it turned the light off. My airbag light is now on, I am going to wait and see if it turns off on its own as it has happened before with moisture in the system however it was not on before the install. All other features in the truck appear to operate normally.

The switch is rather difficult to install due to its shape. It requires a lot of work with a file.

Overall, great writeup, it seemed vague going into the install as I thought there would be more to it but it really is a simple mod just tedious especially if you are like me and hate taking the dash apart.

HenryJ thank you for your time, parts and knowledge.

Post by **HenryJ** » Fri Feb 06, 2009 9:51 am

Awesome! So the Tow/Haul works? What do you think of it?

The air bag light sounds strange? Check the fuse. My airbag light is on all the time, but that is because the fuse is pulled. I have a laptop sitting in front of the passenger side module and don't want it to make the laptop a projectile in a deployment.
I never checked to see if it would be lit with the fuse installed like yours is. Might be something I overlooked?

I better go check mine. :speedy:

killian96ss · Post by **killian96ss** » Fri Feb 06, 2009 10:12 am

FYI, (for those that don't know) when the air bag light is on it means the system is disabled (air bags will not deploy in an accident).

Steve

Post by **HenryJ** » Fri Feb 06, 2009 2:43 pm

Good to note that cold weather and brittle plastics can be a problem. While removing the second BCM I broke the retainers too. I had little choice as the dash was folded down a little and I too did not fully remove the cover panels.

green02crew wrote:My airbag light is now on, I am going to wait and see if it turns off on its own as it has happened before with moisture in the system however it was not on before the install.

This is why having a second install is great! I would have never known. Looks like mine is on too. A bonus for me as I do not want the bags to deploy with the accessories I have mounted in front of them.

We will have to figure out what needs to be done to enable them though, as having the SIR is a benefit for most.
Not as easy as it once appeared, huh?

Every mod deserves another

I wonder what else we will find? Is everything else working for you? This is the first thing that has come to light as not being a match.

green02crew · Post by **green02crew** » Fri Feb 06, 2009 8:31 pm

Yes tow/haul does work! Shifts firmer than my firmer shifts by just a little. It does allow the transmission to shift into OD which I did not expect. It will help with the 4 place enclosed snowmobile trailer this winter.

The retaining clips broke with me just unhooking them, very little pressure applied. The dash was similar, just by pulling it out of the way, thankfully in a spot that makes no difference and is hidden by my electric brake controller.

I did notice a small difference with the new BCM other than airbag light, when I unlock with the remote it only flashes once not twice like it used to and the interior light does not illuminate for as long a period of time as it did after closing the door and locking. No large changes there. Everything else appears to operate normally.

In speaking about security, the truck started with a new BCM no problem, not much security in my mind.

And I wonder how to get the airbags back

Post by **HenryJ** » Fri Feb 06, 2009 8:43 pm

I'll have to check out the lights. I had not notice a difference there.
You are right it does go into overdrive. It has to be past 55 mph though. All the changes are below that I guess.

I am not too worried about the SIR right now, but I will check out the terminals to see if they are the same, or if there is something else.
I too look forward to have the towing ability. It really should make a huge difference.

green02crew · Post by **green02crew** » Fri Feb 06, 2009 8:54 pm

I am not worried about the airbags at this point. My girlfriend is too short for them anyways so it is good to have them disabled when she is riding. I am more curious why they would be disabled and how to turn off the annoying light

Post by **HenryJ** » Fri Feb 06, 2009 10:13 pm

Ok, Fighting HAL again

He knows what we did!

I would bet that if scanned we get a DTC B1001
"The restraints ID stored in the SDM does not match the restraints ID stored in the BCM, or the VIN stored in the SDM does not match the VIN stored in the BCM."

The test is run during initialization.

Light is set and system disabled.

Looks like I need to gather the matching SDMs as soon as I get the chance.

04crewvt · Post by **04crewvt** » Sat Feb 07, 2009 6:03 am

Looking on line at a few places it looks like the Tech II scanners are needed to reset the SDM when system parts are replaced. Hopefully changing out the unit will fix the ABS system but another warning is that when powering up SDM after replacement air bags have been known to deploy from a voltage spike so be very careful when replacing. SDM for those that don't know are the "Black Boxes" for crash data.

The benefit of retrieving data from flight data recorder using the Black Box was only available to airlines for many years. This invaluable instrument, which helps determine what happened in the critical time before a crash, is now available as Airbag SDM crash data retrieval system on GM cars.

In response to the call of the National Transport and Safety Board (NTSB) in 1997 that vehicle manufacturers and the National Highway Traffic Safety Administration team up to gather information on vehicle crashes using on board collision sensing and recording devices, General Motors expanded the data downloaded to permanent memory in the air bag sensing and diagnostic module at deployment or in a near deployment collision.

The capability to record pre-crash data has since expanded with time and technological advancement. General Motor's Vetronix crash data retrieval tool (CDR) collects vehicle crash data via the air bag system SDM.

General motors together with Vetronix Corporation developed the Vetronix CDR System, which downloads the data stored in recordable airbag modules.

Software, hardware and interface cables allow recorded data such as Delta V, driver seat belt usage and pre-impact data to be downloaded to commonly used computers in easy to read format. Interface cables that connect directly to the airbag module are available for vehicles that cannot be powered up after a crash.

This new technology then also makes it easy for investigators to input other vital information, like weather conditions, and send the data to a remote database. The final 5 seconds leading up to an accident event is very vital information that can be stored at the airbag SDM module recorder. This process can only be done using the Vetronix CDR equipment and a PC.

Includes most 1994 and newer Chevrolet, GMC, Buick, Oldsmobile, Pontiac, Cadillac, GM trucks, Saturn, and Hummer vehicles have GM airbag SDM recorded data coverage.

Post by **HenryJ** » Sat Feb 07, 2009 7:09 am

That does bring up an important point. The SDM from a salvage yard may already have crash data stored. Hopefully they do not lock out functions after this.

04crewvt · Post by **04crewvt** » Sat Feb 07, 2009 7:14 am

According to what I was reading a SDM with crash data can not be used again until the unit crash data is removed. They are basically a one time use recorder that needs reprogramming or replacement after a crash. If you are going to that length might as well have someone with a scanner do the SIR reset procedure.