2005 Tahoe "Service 4WD"

[SLCHOE]

There is a harness upgrade (superceeded p/n) for these trucks and this sounds like one of the ones I spent a bit of time on before I called the dealer and found out they had harnesses that would get wet and dirty and cause issues like this. Call the dealer and see if your truck falls within the TSB or post your vin# and I can post the info for you.

---------- Post added at 10:20 PM ---------- Previous post was at 10:16 PM ----------

One other thing is to check the tires sizes. make sure all 4 tires are the same size. Differing tire sizes will cause issues within the 4wd system.

---------- Post added at 10:28 PM ---------- Previous post was at 10:20 PM ----------

15306187 is the part number for the harness for the transfer case speed sensor wire harness update which fails at the connector if it has been disconnected in previuos services. This causes loosenes and thus inaccurate or null readings from the sensor.

This would also cause code C0374

---------- Post added at 10:33 PM ---------- Previous post was at 10:28 PM ----------

Check the transfer case speed sensor wiring. They can get messed up if someone has ever disconnected them. There is an updated harness also from a TSB for this vehicle from GM. The updated harness part number is 15306187. Check the wiring first. If its messed up, fix it.

 

[Opus62]

There is a harness upgrade (superceeded p/n) for these trucks and this sounds like one of the ones I spent a bit of time on before I called the dealer and found out they had harnesses that would get wet and dirty and cause issues like this. Call the dealer and see if your truck falls within the TSB or post your vin# and I can post the info for you.

---------- Post added at 10:20 PM ---------- Previous post was at 10:16 PM ----------

One other thing is to check the tires sizes. make sure all 4 tires are the same size. Differing tire sizes will cause issues within the 4wd system.

---------- Post added at 10:28 PM ---------- Previous post was at 10:20 PM ----------

15306187 is the part number for the harness for the transfer case speed sensor wire harness update which fails at the connector if it has been disconnected in previuos services. This causes loosenes and thus inaccurate or null readings from the sensor.

This would also cause code C0374

---------- Post added at 10:33 PM ---------- Previous post was at 10:28 PM ----------

Check the transfer case speed sensor wiring. They can get messed up if someone has ever disconnected them. There is an updated harness also from a TSB for this vehicle from GM. The updated harness part number is 15306187. Check the wiring first. If its messed up, fix it.

Most interesting. Could explain the intermittent nature of the appearance of the "Service 4WD" message. Sometimes right at start up, sometimes a half hour later. There was a warranty repair done on July 5, 2011, "Transfer case two/four wheel drive actuator position sensor replacement"

My VIN is 1GNEK13T65J149419

 

[Opus62]

My ELM327 OBD2 bluetooth interface arrived a few days ago.
After some long searching, I found an Android app that would let me see ALL codes, not just engine codes. And it worked! I have a code C0306 which is "Motor A or B circuit failure". Code C0306 is set once the Transfer Case Control Module detects an open, short-to-ground, or low voltage in the Motor Control A or B circuit, or an open or short-to-ground fault inside of the transfer case motor. Which could easily be a bad connector.
I also got the code for my "Service Air Bag" message and light on the DIC. That code is B0103 which is for the right side front impact sensor.

I love my $10 dongle and $6.00 app.

 

[eeehabt]

Hi,
Any updates about your truck? I have a problem now after having fixed the 4wd system. My truck is Yukon 2007. Its behavior was not switching between drives. It stayed on the 2wd. Light blinked but returned to 2wd. After some aftermarket friends' advice, I changed the actuator on the front differential and it was like magic, but I didn't drive-test it because the X owner had different tire sizes installed on the vehicle. After I changed the tires, I went to the beach and I needed the 4wd for only two meters to reverse up a tiny sand hill. Every thing was just fine until I wanted to leave. I disengaged the 4wd as it was no longer needed, but I immediately got the Service 4WD light, and the new problem now is that it wouldn't stay on 4WD Auto. It shifts between the other options but never the Auto mode. I have a Launch Master Scanner, but didn't have the mood to hook it up and see where the problem is. My question comes to the experts now: Do I need to let the PCM learn the new part I installed? And yeah, I disassembled the shifter on the transfer case and checked it for defect. The only thing wrong was loose screws. I tightened them and reassembled, and that was before I changed the actuator.

 

[bret04yuk]

try putting the transmission in neutral, then press the 2HI button, should hear the transfer case disengage.
(my yukon is AWD and doesnt have the option of 2HI, but when pulling someone out of the ditch or mud, thats the only way it will come out of 4LO and back to AWD)
if that doesnt work check the code. im from northern MN and on really cold days my "service 4wd" message appears and goes away after a few miles when i believe the fluid heats up. it also likes to piss all of its coolant out at -30*F and overheat, which is kind of an oxymoron, turns out a pesky cracked coolant hose.

 

[eeehabt]

try putting the transmission in neutral, then press the 2HI button, should hear the transfer case disengage.
(my yukon is AWD and doesn't have the option of 2HI, but when pulling someone out of the ditch or mud, that's the only way it will come out of 4LO and back to AWD)
if that doesn't work check the code. I'm from northern MN and on really cold days my "service 4wd" message appears and goes away after a few miles when i believe the fluid heats up. it also likes to piss all of its coolant out at -30*F and overheat, which is kind of an oxymoron, turns out a pesky cracked coolant hose.

SOLVED
Thanks for the clarification and for making me laugh at your car peeing the coolant. The temperature here is the opposite to your location. Actually, we don't need to warm the engines in the morning. Anyway, the update on my truck is that I hooked up a "Launch" scanner tool to the truck and started searching for any related diagnostics for the 4WD. I could only find for the transmission solenoids relearn. I chose that option and it took about 5 minutes. Then I disconnected the scanner and the truck now is OK. So, in case any of you guys changed a major part in the 4WD system, find someone with a descent scanner that is capable of programming, like the Tech 2, and let your truck relearn that new part. I hope that would help.

 

[Opus62]

Success!!!!

Been away for a while [busy in the RV industry, slowing down now]. Did some investigating. A and B circuit wires show clean continuity from the connector at the encoder motor up to the TCCM. Decided to order an encoder from Rockauto, my favorite online parts source. A quick parts swap, easy peasy! And now <drumroll> I now have 4 wheel drive! WOO HOO! No "relearning" required. No need to plug in any kind of scanner. It's good to win a battle or two WITHOUT breaking the bank.