how our s-10's 4x4 works

williamcstonejr · Post by **williamcstonejr** » Thu Feb 21, 2008 5:52 pm

I have run search after search and at this point I cannot find anything in here that pieces our 4x4 system together completely. I do not mean a detailed manual just when I push that button on the dash what happens (Condensed version) from start to finish. I have manuals coming but I am sitting home due to rain and have the time to poke around my truck before I go back to work next week. To look for any bugs I can tackle now while I have the time. If it is in here can somebody point me in the right direction? If it does not anybody know?
Am I the only one who is currently scratching their head on this? I assumed there was a switch someplace under the hood that opened vacuum to the transfer case which relayed this vacuum to the vacuum actuator. Today I was working on my truck and noticed a switch on the front diff that I did not know about. Now I am scratching my head thinking WT*&^$.
Brule if this is too much to ask just delete this and I will wait till my manuals get here. I’ll understand.

Post by **HenryJ** » Thu Feb 21, 2008 6:03 pm

You have a button on the dash, a module in the right kick panel , a motor on the transfer case, a vacuum switch on the transfercase, a vacuum actuator under the battery, a switch on the front axle.

You push the button, this tells the module what you are requesting. It tells the motor on the transfercase what to do. Once it moves to four wheel drive it activates the vacuum switch mechanically, this sends vacuum to the actuator under the battery that moves the cable to the front axle. Once the shift fork in the front axle moves it actuates a switch to tell the system the front axle / 4x4 is engaged.

williamcstonejr · Post by **williamcstonejr** » Thu Feb 21, 2008 6:20 pm

My old vacuum actuator is sitting on the desk of the body shop right now, when I push my 4x4 buttons I can hear the transfer case engage and all of my lights (Pertaining to the button pushed) stays solid as if I was in 4x4 with no issues, should this be?? I would think by what you are describing I should currently have a blinking light on the dash telling me I have a problem.

Post by **HenryJ** » Thu Feb 21, 2008 6:34 pm

I believe that the lights on the switch only relate to the encoder motor and shifting of the transfercase.

williamcstonejr · Post by **williamcstonejr** » Thu Feb 21, 2008 6:43 pm

That’s good to know. My 4x4 worked just fine after the accident, didn’t have a problem until I got it back from the body shop. The owner is now ordering me the vacuum actuator and I am installing it myself to avoid future downtime/problems. Thank you for the good info as usual!!!!!!!
When I get my manuals hopefully I will be more of a help around here instead of a parasite fishing for free advice.

Post by **HenryJ** » Thu Feb 21, 2008 7:11 pm

We are all here to help where we can. Use several sources and do not take one as gospel. Manuals can be and are wrong. People make mistakes and have wrong answers too.
I have said it before: There are no stupid questions, only stupid people...who do not ask questions.

williamcstonejr · Post by **williamcstonejr** » Thu Feb 21, 2008 7:18 pm

Once the shift fork in the front axle moves it actuates a switch to tell the system the front axle / 4x4 is engaged.

So does this mean that since my actuator is missing thus no cable movement, I would get a code from the computer if I hooked up to it?

A very sincere THANK YOU.

williamcstonejr · Post by **williamcstonejr** » Mon Mar 03, 2008 11:50 am

While I was waiting for my actuator to come in I ran my truck in 4x4 just to insure I didn’t have any transfer case issues. As I stated before the lights where continuous and I was questioning (unsure) the role of the front axle switch. Since I had a solid light on the dash (4x4 buttons) I assumed that I should get a trouble code telling me that the front axle was not engaging. I purchased a cheapo scan reader only on sale today and I have no codes, everything is operating normally. Just to be sure I took my truck to my old Marine buddy that runs his own shop and hooked it up. Sure enough everything is working fine and the cheapo scanner was correct. So at this point I am asking since I have installed my actuator and run my truck in 4x4 several times did the code reset or did I ever have a code??? Does anyone know? I have been researching this for a week and cannot come up with anything. My only question I guess is if this switch does not set any codes what purpose does it really serve in the first place? If nobody knows I will disconnect the switch this weekend, run it in 4x4 a couple of times and connect the scanner to see what I come up with. Thanks,

Billy

green02crew · Post by **green02crew** » Mon Mar 03, 2008 11:54 am

The computer prob does know there was an issue because as far as it could tell, the truck was in 4x4.

JaVeRo · Post by **JaVeRo** » Mon Mar 03, 2008 12:08 pm

My understanding of how it's supposed to work (which is probably wrong but just food for thought)

You will not get any codes that can be read with a scanner. The only codes that may show up will be indicated by the selector switch lights flashing. They are stored in the transfer case control module and not connected to the main computer (PCM).

From what I have been told, your lights will not indicate you are in 4wd unless everything is working properly including the front actuator. That being said, I have found on mine that the front actuator can malfunction and the lights will still indicate 4wd. Same as what you have found.

My theory is (and it's only a theory from a shade tree mechanic) when the switch on the front differential malfunctions, it sticks in the 4wd position. While in 2wd, the lights show 2wd due to the transfer case.

A way of checking it would be to use an ohm meter on the front switch while someone is pulling and pushing the cable engaging the front axle.

ICBW MWSIUA

James

williamcstonejr · Post by **williamcstonejr** » Mon Mar 03, 2008 1:49 pm

JaVeRo wrote:A way of checking it would be to use an ohm meter on the front switch while someone is pulling and pushing the cable engaging the front axle.

ICBW MWSIUA

James

Thanks for the advice green02 and James. Or instead of taking that battery out to pull the cable I could just disconnect the switch push the four wheel drive button to see if the lights flash.

roadrunner · Post by **roadrunner** » Mon Mar 03, 2008 1:56 pm

You fellas need to reread Brule's post in this thread CAREFULLY. It is the second post in this thread and is a very good explanation of how the electric shift functions on our CC's.

williamcstonejr · Post by **williamcstonejr** » Mon Mar 03, 2008 2:13 pm

roadrunner wrote:You fellas need to reread Brule's post in this thread CAREFULLY. It is the second post in this thread and is a very good explanation of how the electric shift functions on our CC's.

I did. Reread MINE carefully. What the _____ purpose does this swith serve? Yeah it lets the system know

HenryJ wrote:Once the shift fork in the front axle moves it actuates a switch to tell the system the front axle / 4x4 is engaged.

How do you diagnose a problem with it? The lights don’t flash because that has to do with the transfer case motor. I just ran my truck with the switch disconnected in 4x4 up and down some trails around here, truck worked fine and no codes. Basically the thing is useless as far as I can tell. I am just trying to figure out this switch, what purpose it really serves and how to diagnose a problem with it if you have one because you can disconnect it and run the truck and never know. My truck works fine I just never got a solid answer on this topic and it will drive me nuts till I find out.

Edited - Not yelling at you roadrunner, I just read what I wrote and it sounds hostile. I am Yelling at the situation, when something like this gets in my head I dont let it go until I get the answers.

Billy

roadrunner · Post by **roadrunner** » Mon Mar 03, 2008 2:39 pm

I've had a "run in" with that switch you're talking about detailed in another post on the forum. What happened on mine was the switch was too sensitive and would cause the 4x4 to shift on it's own if I hit a slight little bump. It is my understanding that the lights on the dash switch won't properly indicate whether or not you are in 4x4 and front diff engaged if this switch doesn't work properly. You say you ran with it unhooked? Did your dash switch lights function properly while you did that? Your owners manual describes how these lights should act on startup when the system is functioning properly. Also goes through a procedure you can use to "force" the system to shift if it won't on it's own. I can attest that if your actuator motor on the transfer case isn't working properly this "force" shift won't work.
I beleive there have been other posts on how to read transfer case codes (by counting blinks of the dash switch lights) also posted. Lacking that you have to go to a shop where they have a drivetrain scanner to read any transmission or transfer case codes as common OBDII scanners aren't capable of reading them. (Most of them anyway)

Edit: If you want to go look at the transfercase codes and how to read and trigger them you should go to Stock Mechanical Drivetrain listed under Stock CrewCabs and there is a good sticky there under Transfer Case Codes.

Didn't presume you were mad just frustrated. Been there. Done that. I only went into a lengthy explanation trying to help. I ain't mad either.

williamcstonejr · Post by **williamcstonejr** » Mon Mar 03, 2008 3:40 pm

The diagnostic trouble codes are displayed on the three transfer case shift select buttons. The shift select buttons are located on the instrument panel when the connector pin 13 on the data link cable is grounded, and the ignition switch has been OFF for at least five seconds prior to positioning the ignition switch to run the shift select buttons will blink various times together in order to indicate a diagnostic trouble code from 1 to 4.
Position the ignition switch to OFF. Ensure the ignition switch is positioned to OFF for at least 6 seconds.
Connect pin 13 on the data link cable to a vehicle ground source. The data link connector is located in the cab under the instrument panel on the drivers side.
Position the ignition switch to RUN.
Note the shift select buttons for blinking codes. Refer to Diagnostic Trouble Codes .
If the shift select buttons all blink one time and stop, and do not continue to blink, no fault codes are stored in the TCCM.

I read the above after reading this:

JaVeRo wrote:You will not get any codes that can be read with a scanner. The only codes that may show up will be indicated by the selector switch lights flashing. They are stored in the transfer case control module and not connected to the main computer (PCM).

So that’s when I disconnected the switch went on a short 4x4 trip used a paperclip and jumper (On the trail with switch still disconnected) grounded out number 13 and got all three lights blinking and going out indicating no fault codes. This was while the switch was disconnected and doing a little 4 wheeling. And I followed the directions, Key off Short the connecter turn to run. Brule sorry for eating up precious server space lets just delete this whole thing. I will go to the dealer and be a major pain until I get my answers. If anyone is interested in the results just say so and I will post em when I get em.

Billy

roadrunner · Post by **roadrunner** » Mon Mar 03, 2008 3:54 pm

Hey man! We all always want more info. That's a good thing. Sorry if I wasn't able to help ya.

I was tryin.

williamcstonejr · Post by **williamcstonejr** » Mon Mar 03, 2008 4:06 pm

roadrunner wrote:Hey man! We all always want more info. That's a good thing. Sorry if I wasn't able to help ya. I was tryin.

Sorry I honestly do appreciate the help. I don’t mean to sound ungrateful so if that’s how I am coming off I apologize. It is just driving me nuts that nobody around here (My town) that owns their own shops can’t answer it, nobody here (On the site) can either. The guys on this site know more about these trucks than the guys that work on them everyday. I think that if anyone ever had a problem other than you with this switch they didn’t even know it. You knew because there was a symptom to the problem I mean seriously when I went wheeling today with the switch disconnected something should have come up on the codes. I guess most normal people would say screw it the truck works and leave it alone but I am not normal. I become obsessed with things I don’t understand and go to great lengths to get my answers. I’m a little crazy that way.

Billy

roadrunner · Post by **roadrunner** » Mon Mar 03, 2008 4:16 pm

I was just reviewing the codes on the sticky post and also remember reading, possibly on a different post, that the tccm may not set a code on a one time or intermittent failure. It will only set a code after a set number of failures. So, it may not recognize a single event such as having the switch unhooked or inoperative until it records the failure several times. Additionally if the system starts working right again the number of correct operations will subtract from the number of incorrect ones also. Trying not to confuse you, but this might explain why no codes with a short interval inoperative switch situation. Might take ten or twenty occurences to set a code.
It still may not set a code for that unless it affects other components in the system also since there is no direct code for a front switch verification failure.
Hope this helps and doesn't confuse the issue further.

williamcstonejr · Post by **williamcstonejr** » Mon Mar 03, 2008 4:30 pm

Now that makes sense! Thanks I guess I didn’t run my searches properly. I have been looking for this answer for over a week. I guess its kind of like one of those things “If you stare at it too long” I should of walked away for a few days then maybe it would have smacked me in the face. Thank you, what a relief!

roadrunner · Post by **roadrunner** » Mon Mar 03, 2008 4:36 pm

Glad I and we were able to help!!

JaVeRo · Post by **JaVeRo** » Mon Mar 03, 2008 5:07 pm

I believe this is what roadrunner was refering to on the codes.

From a previous thread wrote:Straight from the service manual:

The transer case encoder motor is an assembly which houses 4 separate channels. These channels are used to indicate to the transfer case shift control module the present gear position of the transfer case or if the tranfer case is in transition between gears. The encoder motor assembly consists of an electonically conductive inner ground ring in contact with a 3 legged wiper arm. Each legs length is such that it makes contact with the conductive regions of the 4 channels. When any leg of the wiper arm is making contact with the conductive area of any channel, the encoder provides a path to ground to the inner ground ring.

During electronic shifting, the transfer case shift control module monitors the transfer case encoder circuit for the proper operating sequence. If at any time during a shift, the encoder changes from one position to any position other than the next possible position, an error counter in the transfer case shift contol module increments by 4. After the counter reaches 32, the transfer case shift control module set a DTC2, a permanent "encoder fault," and reverts to a 2HI to 4LO or a 4LO to 2HI shift pattern only. To guard against a transient, random encoder fault due to vibration, dirt electrical noise, ect., the fault counter reduces by one each time the transfer case shift control module detects a valid encoder value. The encoder must intermittently fail 25 percent of the time for the transfer case shift control module to consider it faulty and store DTC2. It is imperative that the technician test-drive the vehicle and request several shift in order for the code to properly be set.

I think this only applies to faults in the encoder motor. I could be wrong.

James

Post by **HenryJ** » Mon Mar 03, 2008 5:10 pm

Also keep in mind that this is not a sentient truck. It is not going to give you codes for every failure that can occur. There are very few codes for the transfercase and most of them relate to the encoder motor functions.
It may not report a code for the front axle switch at all. That would be my suspicion , as the PosiLok kit does not throw a code when the front axle is not engaged in four low operation.

The front axle indicator does send a signal to the TCM as indicated in the schematics. This may be needed for corrections in the ABS wheel sensors readings as well as a conformation of engagement for the four wheel drive system. You may be able to blow that theory out of the water considering the Bravada doesn't have a front axle actuator swtich. That is muddying the water though since it uses a different transfercase and has a second VSS.

If you wish to test the front axle switch a continuity tester will do that. If you wish to test the wires a voltage tester will do that.

If you need to know how the TCCM functions and what part the front axle indicator switch plays in its function, I would suggest you contact Delphi with your inquiry, as this information and the schematics are not included in service manuals. The TCCM is an assembly and not serviceable, therefore schematics for it are really not needed.

As I understand it , you do not have a problems here other than your curiosity. I would say you may not find much interest in this area. Most just want to know how to fix what is broken. You have not found the group that designed the TCCM here. I would suggest that those who did may be the only ones who do have any interest in exactly how it functions. I would not expect a tech to know, or even believe one who claimed to. If you really must know, contact the maker. Then be prepared to run into dead ends finding someone who cares. The question to you will be , "Do you have a problem with it?" or "What can we do to help you diagnose and fix it?"
We can do that here.
Sorry I have no interest in seeking the "true meaning of the TCCM". I do not mean to be calloused. If I suspected 4x4 problems, I would test the switch. It is easily checked. Then move on.

I would ask , what do you gain with this knowledge? Not trying to be mean here, just thinking energies might be better spent in a direction of more value?

williamcstonejr · Post by **williamcstonejr** » Mon Mar 03, 2008 8:35 pm

My need for knowing is this. I haul around three kids in this truck and after my recent accident I have realized it does not matter how safe I drive. There will always be some Jack (fill in the blank) on the road. Southern California is full of them. Two techs have already suggested to me that they think that it may (not know) but may be tied to the ABS during 4x4 operations. Without writing a book about rain in so cal I’ll say that the freeways do not drain very well during heavy rain and in my area we have had a good amount this year for us. So even if it is not recommended I use 4x4 in heavy rain on So Cal freeways. Since this switch (When disconnected) does not effect drivability and does not appear to throw any codes how many CC owners are driving around unaware that this little item may not be working? Especially since all the techs (Including GM) don’t seem to know what the purpose of this little thing is. If it does not affect anything important WHO CARES, if it could affect ABS or something else that’s important then I do care. So my point is, if it affects ABS wouldn’t most of us want to know that? And I don’t think you are being callous or mean. I think the answer wasn’t in your brain housing group and it is not easy to find so you are indifferent. I was a kid who was beat for taking apart his mothers vacuum to find out how it worked. So that being said this all started for me because I wanted to know what purpose this part served. Then ABS came out of a few techs mouths and I was concerned. I will test it and replace if necessary just in case of possible ABS affects. So what I would gain? Keeping my children as safe as I can by not being indifferent, I don’t feel this is wasted energy or a pursuit of less value. I started this thinking someone would have the answer, sorry I was wrong. You said the only stupid question was the one not asked (Not an exact quote) but then I guess that is conditional on daily attitude and perceived value on the so called question. I just wanted to explain myself to you, so now that I have I will put delete in the subject line tomorrow or you can just do it. It’s up to you. Everyone thank you for your efforts. I do APRECIATE it!

PS I didn’t want to mention ABS until I knew something to avoid being Chicken Little screaming about THE ABS IS FAILING, THE ABS IS FAILING!

PSS I am not angry either just in case it sounds that way. I am annoyed that a mechanic that thinks it may possibly affect ABS performance does not see the value in this question or pursuit.

Post by **HenryJ** » Mon Mar 03, 2008 9:01 pm

It would only affect the ABS to "numb" it to differences in sensor readings due to front wheel spin. I do not see a safety issue with its malfunction. ABS defaults to inactive if there is a problem.
Testing it is very simple. Activate and engage the front axle. Test for continuity. This would take only minutes and then your children could ride with your new sense of security.
Or maybe there is no safety in a motor vehicle?

Looks like it is #4 in the list of most popular ways to die.

williamcstonejr · Post by **williamcstonejr** » Mon Mar 03, 2008 9:16 pm

Touché

04crewvt · Post by **04crewvt** » Tue Mar 04, 2008 4:02 am

I won't speak to how our s-10's 4x4 works but the mechanics you here speaking about ABS and 4x4 are correct in one way. In the older pickups like my 89 Silverado the ABS is linked to the 4 wheel drive system and shuts off when the front axle is engaged, thats because unlike todays 4 wheel ABS in those trucks the ABS only has sensors in the front hubs. I don't know why, I just know from the manual that thats the way it is.

To my knowledge the ABS does work in our truck when in 4x4, at least it seemed to be when I was trying to climb the rock obstacle in my avatar photo. I was using the left foot on brake and right on gas and trying to stop myself at the top of each rock I could feel the ABS let the wheel spin as I slid back down at one point with my foot all the way to the floor on the brake pedal.

If all you are trying to do is test the theory go out on a wet road put it in 4x4 and power brake you will find out for sure if it works just not the why.

Post by **HenryJ** » Tue Mar 04, 2008 8:37 am

I concur. We went over that in this thread : ABS functional during 4wd operation?
It would be my assumption that the input prevents it from disabling or setting an ABS fault code when the wheel sensors detect differences due to an active front axle.

roadrunner · Post by **roadrunner** » Tue Mar 04, 2008 2:53 pm

No need for me to read anything on the ABS function on my 01 CC. I know for fact it works in 4X4 because of a number of times I've cussed it as I "rolled" into or past something I didn't want to.

Plans are currently under way to disable temporarily or possibly permanently. Haven't decided for sure yet.

And Yeah I've read the relavent posts on this topic already.

Post by **HenryJ** » Tue Mar 04, 2008 3:12 pm

roadrunner wrote:...Plans are currently under way to disable temporarily or possibly permanently.

Pull the fuse. That is what I do with the SRS too.

roadrunner · Post by **roadrunner** » Tue Mar 04, 2008 3:16 pm

[/quote]Pull the fuse. That is what I do with the SRS too.[/quote]

That gonna leave the light on? So far I kinda like the idea of a switch for selectivity.

Post by **HenryJ** » Tue Mar 04, 2008 3:29 pm

Yes light on.

roadrunner · Post by **roadrunner** » Tue Mar 04, 2008 3:36 pm

HenryJ wrote:Yes light on.

Drat!

I was afraid of that. Guess I could do what I read in another post here, put a you da man! sticker over the light.

F9K9 · Post by **F9K9** » Tue Mar 04, 2008 4:52 pm

Leave the light visible. It will remind you to enable it when finished wheeling.

Post by **HenryJ** » Tue Mar 04, 2008 5:07 pm

My thoughts exactly.

roadrunner · Post by **roadrunner** » Tue Mar 04, 2008 5:15 pm

More fun seeing a sticker all "lit up" though.

Seriously though the three things I regret having most on my CC are the electric shift, ABSbrakes, and rear disc brakes.