TCCM Codes

Hi,

If you let me know the codes you found, I may be able to help. There are a few issues falling under TSB's that are related to wiring problems when I look up the TSB you mentioned. If you look at pic 1, see if you feel if any of these may benefit you.

The remaining two pics are the wiring schematic you requested. I had to cut it in half to make it readable, but I did overlap them so you can follow from one to the next.

Let me know if this helps or if I can help in any way.

Take care,

Joe

See pics below.

Thanks Joe,

These are what are in it currently. Sure looks like the chaffing bulletins might help. The 4wd indicator works, at least the lights change, and it does go into 4wd lo, it just stays in 2wd.

U0131_71 Lost Comm with PS
C0374_54 General System Performance Temp High
U0073_71 Control Module comm bus A off invalid serial data received
C0379_02 Front axle system short to ground
C0379_04 Front axle system open
B0770_01 4wd indicator circuit short to battery
B0770_06 4wd indicator circuit short to ground/open
B0775_01 Four-Wheel drive high range indicator circuit short to battery
B0775_06 Four-Wheel drive high range indicator circuit short to ground/open
B0780_01 Four-Wheel drive lo range indicator circuit short to battery
B0780_06 Four-Wheel drive lo range indicator circuit short to ground/open
B0785_01 Two-Wheel drive high range indicator short to battery
B0785_06 Two-Wheel drive high range indicator short to ground/open

Hi,

The one code that sticks out to me the most is the U0073 71. That indicates a problem in the ECU high-speed bus communication which inhibits the setting of all other communication DTCs.

The idea of 2wd low range is tied into the front system codes. I suspect we need to check the can.

I attached the wiring schematic of the information bus. The system contains a few wires that run between computers/modules. The primary wire colors related to the transfer case control module are tan and tan wire with a black tracer. I would start at the TCCM. Inspect the connectors at those wires for damage.

Note: The TCCM is located under the dash on the left side which is where wiring damage has been identified in the TSB.

Let me know what you find.

Joe

See pics below.

So, the issue of 4wd not working was found and corrected. While looking at connectors, I was under the front axle and noticed the RF stub shaft was out of the housing a bit too far. I pushed it back in and I was able to engage 4wd. Still had lot of codes. There are 2 thin washers on the shaft that get bent after a while or if someone tries to pull this shaft out like it was a CV axle. To pull it out, the housing must come off and a clip removed. The replacement washer is thicker and replaces the 2 washers. I changed the outer seal as well. What about all the codes? Having a short to battery and short to ground on the same circuit, that worked, is very odd. Having no 'Service 4wd' message was also odd. It makes no sense. Also, while the vehicle was in the shop, the engine module set 15 codes, some being O2 response. These also made no sense since the vehicle had not been driven and O2 response needs vehicle speed for a period of time to run its test. The codes would clear, however. I was using a foxwell NT624 scanner I got off amazon. It worked well enough but also had issues connecting to older vehicles that used non-CAN protocols. I had a friend come over with a snap on scanner and we found that the transfer case actually had no codes!! I have a OBD port Y cable so with both scanners reading the same stream, the foxwell would show 13-15 codes and the snap on, None! So I am done with the codes, returning the scanner (love amazon), getting a newer version and working on a noise from the flywheel area. Thanks for the schematics Joe, I didn't have to use them much but your help led me to the right diagnosis.

Hi,

First, you are very welcome. I'm glad to hear you found the issue. So, if I understand correctly, your scanner indicated codes that didn't exist?

Regardless, I'm glad you are back in business. Please feel free to come back anytime in the future if you have questions.

Take good care of yourself.

Joe

Yes, the scanner is looking at something incorrectly. I returned the first one and got their higher level one and it does the same thing. I am getting O2 response codes without the vehicle even moving and those need a cruise for a while to set.

On another note, the washer fix did not last. It looks like the clip is worn enough it won't hold and the axle is coming out again. I haven't torn it down again. Do you know the GM PN for that clip on the right front stub shaft?

Hi,

Are you referring to the output snap ring? Take a look at pic 1 below. If that is what you are referring to, look up GM part number 30026-06097523

Tell me if that looks like the snap ring you are referring to.

Joe

See pic below.

That is but the number you gave is an AC Delco part number. Do you know the GM one? It would only be 8 digits.

Might be 25931953.

Hi,

AC Delco is the primary OEM parts manufacturer for GM. The number you have is likely the manufacturer's number and the one I provided is AC Delco's number for the same part.

The number you provided is a valid number as well.

Joe

The groove in the axle where the ring sits was worn, and the washer would push the ring out of the groove. Rather than buy a new axle, I filed the groove and made it as square as possible. I also filed a chamfer in the id of the thick replacement washer as it did not have one like the original. It looked good and seemed like it was going to work but I decided to tac weld the ring onto the axle for some insurance. If it doesn't work, I need an axle anyway. https://youtu.be/yfnEHSDKBZ4 Listen at the beginning and end of the video for a tinging noise, which is next. I know what it is, what is your guess?

I'm glad to see it's working. Driving around in the field looks like fun. LOL

I did hear a noise at the end of the video but couldn't identify it. It's very hard for me to hear. Is it something with splines?

Joe

No, the spring in the starter solenoid must have broken. The starter gear doesn't retract, and it is bouncing off the flywheel. I already had the starter out and verified it. I just haven't got the new one to change it yet.

LOL I never would have guessed that. Honestly, anything that can go wrong, will.


Take care and I loved the video.

Joe