Code Reader for the NP236/246 Transfer Case

[JaVeRo]

Does anyone know of a scanner or computer based software like AutoTap that will read the DTC,s on the automatic (4 button) transfer case. The 1500 Silverado work truck I drive keeps giving a "Service 4WD" message. I am reasonably certain it is a loose or weak wiring connection as it only happens on rough or washboard roads and has nothing to do with actually selecting 4wd. Knowing what code it sets may help locate the bad connection.

The Service 4wd message goes away at the next cycle of the key. I don't know if the codes are stored. It's a company owned truck so I can't just pull into a dealer anytime I want unless I want to pay for it out of my pocket. Taking it to the company shop would be like taking my PC to a bicycle shop.

Thanks,
James

[HenryJ]

What year is it?

[JaVeRo]

Sorry,

It's a 2006 Silverado 1500 Automatic with the 246 (4 button) transfer case.

[HenryJ]

They used some really brittle wire in the early to mid 2000 models. Fewer large strands that break with movement over time. Wiring needs to be secured to prevent movement.

Address TSB # 05-04-21-003.

Subject: Service 4WD Light Illuminated, DTC C0374 Set (Inspect Wiring Harness to Transfer Case Speed Sensors, Replace Wiring Harness) #05-04-21-003A - (03/03/2006)

Models: 2004-2006 Buick Rainier

2003-2006 Cadillac Escalade Models

2003-2006 Chevrolet Avalanche, Silverado, Suburban, Tahoe, TrailBlazer, TrailBlazer EXT

2003-2006 GMC Envoy, Envoy XL, Sierra, Yukon, Yukon XL

2003-2004 Oldsmobile Bravada

2005-2006 Saab 9-7X

with Four Wheel Drive or All-Wheel Drive

and Active All-Wheel Drive (RPO NP4) or Active Two-Speed (RPO NP8) Transfer Case


This bulletin is being revised to add the 2006 model year, Saab 9-7X model and clarify model usage information in the Correction section. Please discard Corporate Bulletin Number 05-04-21-003 (Section 04 -- Driveline/Axle).

Condition
Some customers may comment on intermittent illumination of the "Service 4WD" light. Upon investigation, the technician may find DTC C0374 set. The customer may also comment on intermittent erratic operation of the 4WD or AWD system after driving through rain/snow or simply going through a car wash.

Cause
The speed sensor signal may have become corrupted. Possible openings in the speed sensor wire insulation (twisted pairs) can allow water intrusion. Also, wire connections contaminated by water may result in short circuits and erroneous speed sensor readings. This most often occurs on the rear speed sensor circuit.

Correction
Inspect the wiring harness to the transfer case speed sensors. On Rainier, TrailBlazer, Envoy and 9-7X models, fabricate a replacement speed sensor harness between the C101 connector and the speed sensors. Refer to Speed Signal, Front Axle Actuator, and Indicators schematic in SI. Replace the affected twisted pairs. Do not over-twist the two wires in the replacement harness. Use service connector pack, P/N 88987183, at the speed sensor end and terminal, P/N 15326267, at C101.

Terminal testing tools and service terminals can be found in Terminal Repair Kit J 38125. Terminals are available from SPX/Kent-Moore. Call 1-800-GM-TOOLS (1-800-468-6657).

The smaller transfer case harness splices into the larger chassis harness a few inches in front of the crossmember. The chassis harness routes along the left side of the frame under the driver door area. Use nylon tie straps to secure the fabricated harness to the main chassis harness between the transfer case and C101.

On the full-size pickup and full-size utility models, replace the 2.2 m (88 in) pigtail harness that runs from the C151 connector under the hood to the transfer case. Use either harness, P/N 15224661 or 15224663, depending on vehicle equipment. Refer to Propshaft Speed Sensors, Front Axle Actuator and Transfer Case Shift Control Switch schematic in SI.

Important: Technicians should verify the integrity of the splice joints after the repair. All splice joints and connections should seal properly against water or a repeat condition can occur.

Parts Information
Part Number
Description

15224661
Harness Asm-Transfer Case Sel

(4WD Full-Size Pickup/Utility w/NP8 and without Four Wheel Steering (NYS)

15224663
Harness Asm-Transfer Case Sel

(4WD Full-Size Pickup/Utility w/NP8 and Four Wheel Steering (NYS)

88987183
Connector-w/leads, 2-way, Female (Speed Sensor)

(All Vehicles)


Warranty Information (excluding Saab U.S. Models)
For vehicles repaired under warranty, use:

Labor Operation
Description
Labor Time

N6630
Wiring And/Or Connector-Transmission/Transfer Case/Transaxle/Front and Rear Axle Control - Repair or Replace
Use published labor operation time


Warranty Information (Saab U.S. Models)
For vehicles repaired under warranty, use:

Labor Operation
Description
Failed Object
Fault/Reason
Location Code
Warranty Type
Repair/Action Code
Labor Time

3714901
Wiring And/Or Connector-Transmission/Transfer Case/Transaxle/Front and Rear Axle Control - Repair or Replace
37149
67
0
01
01
Use Published Labor Operation Time

The next suspect would be the switch. Those are known to be a problem too.

[HenryJ]

I have used the Equus Innova diagnostic scanners as an inexpensive tools for diagnostic work. By inexpensive, I mean around the $100 mark. I can not say for sure it will read the codes that you need in this case. Higher dollar units will for sure, but I'm not sure it is worth another $500.
I would say that the 3130 model is not a bad tool to have available.

[JaVeRo]

I had emailed Equus a few days ago and this is the response I got.

"Our code readers are designed to read the powertrain system that turns on the check engine light. The powertrain system on OBD2 vehicles have to follow certain rules, where the manufacture still uses whatever they want for the other systems such as Transfer case code and Air Bags. Our readers will not access the Transfer case codes, Air Bags or body codes unless they are causing the check engine light to illuminate. To read and erase these codes you will need a high end scan tool with the correct software for your vehicle."

The TSB you posted is quite likely my problem as it explains another problem I have been having. I have a NiteStar DMI in this truck for measuring distances on jobsites. It connects to the VSS and I recalibrate it anytime I change tires or air pressure. This is the fourth vehicle I have used this on but it has never worked right on this one. It measures fairly accurately if I stay below 30 mph but anything above that starts giving errors. Noise in the twisted pair from poor wiring would explain both problems.

Thanks for the info.
James

[JaVeRo]

Just an update.

I never found a code reader that would read the transfer case codes. The problem I was having last September went away when I finished the job I was on that had me pulling a trailer with a Kawasaki Mule every day. I am guessing it was the increased vibration from pulling the trailer. The problem started coming back about a month ago. I could crank it up and sometimes it would show the correct gear/range on the transfer case, sometimes it wouldn't . When it didn't, I could usually kill it and crank it again.

Last week I took the transfer case encoder motor off and replaced the transfer case range selector position sensor (ac delco 88962315). I didn't know the sensor could be replaced until I found this article:
http://www.fullsizechevy.com/forum/gene ... -pics.html

Now it works like a charm and it cost less than just having the codes read at the dealer. Apparently about 2003 the design changed adding a separate sensor. This one works on the np246 (4 button) transfer case. I tried searching to see if they had one for the np233 or np236 transfer case but so far, no luck.

Since there are several here that have upgraded to full size trucks, I thought I would post this.

James

[Serge PETIT]

Because of the difficulty to find , in France , shops with the Tech2 (only one place in Paris .........meaning very expensive if you need a non powertrain code reading ........!!!!) we are investigating with one friend for purchasing these softwares
http://www.scantool.net/software/scanxl-pro.html
http://www.scantool.net/ppe-software-comparison.html
Plus the GM addons
http://www.scantool.net/software/scanxl ... dd-on.html

but we are searching about custumers satisfactions before investing in these softs ....................

[JaVeRo]

I looked at some of the software last year. To be honest, I didn't know enough about it to even make an attempt at an informed decision on which to buy. If you get it, keep me informed on what you think.

James

[HenryJ]

Smart Phones have come a very long way. My brother has an adapter to connect to the diagnostic port. Any good apps out there?

[Serge PETIT]

I looked at some of the software last year. To be honest, I didn't know enough about it to even make an attempt at an informed decision on which to buy. If you get it, keep me informed on what you think.

James

Sure that I will do !

[HenryJ]

Bluetooth diagnostic port reader and app for smartphone: Torque Lite
If you have a bluetooth capable Smartphone, this looks like a great solution for about $15 US
Ordered mine just now.

[Serge PETIT]

This system is very popular in France and one of my sons use it in an AUDI and is satisfied ; but it indicate only the powertrain DTC, nothing about gearbox , brakes or ACC codes .

[HenryJ]

True, true. I don't know of any affordable solutions for drivetrain and body codes. Good thing that those are less likely cause drive-ability problems or activate the MIL.
You can monitor VSS readings and other sensors to help diagnose what might be an issue. I have had a couple times where the DTC code readers did not solve my problems and I needed the assistance of the dealers Tech2. Those are rare and very far between.

I would love to have a Tech2 and EFI live, There is no way I can justify the expense though. I have AutoTap and found that very useful. The bluetooth interface is a bit of a novelty. It will be fun to have around, but the Bully Dog programmer I am running in the Avalanche will do all I need really.