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Service 4wd

sareljr

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sareljr Enthusiast

sareljr

Posted
Posted

Hey, I just bought an 05 2500HD with the 6.0 Vortec, and I love it! I only have one concern, every once in a while a service 4wd message comes on, an sometimes it tries to go into 4 low by it self so you have to stop and shut down the truck to get it back in 2wd. I have heard that some saughtering comes loose or cracks inside the dash button select assembly. Is this something you can fix one afternoon or do I need a new button assembly?

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

you have a trouble code in the TCCM,

 

have it scanned with a real scanner and return here and tell us what it is

 

no guessing

 

welcome to the site !!!!

5Alive Enthusiast

5Alive

Posted
Posted

And not just any scanner will read that code, since the TCCM is not a federally mandated module that needs to be universally compliant with the OBDII protocol.

 

Repeat: A generic OBDII scanner will NOT be able to read the trouble code you are looking for with the transfer case that is causing the Service 4WD message to appear. The code set is a GM proprietary chassis code, so you will need a Tech 2 or like govtech4 said, a "real" scanner to get your code.

 

Alternatively, if you have an active OnStar subscription, you can press the OnStar key and have them read you every single number on their screen after they scan your vehicle. The OnStar operator will more than likely not understand what he or she is reading, but they don't have to. Listen for any number that sounds like "C03xx", where xx will most likely be the number 27. The "C" stands for "Chassis" codes... in other words, the codes that the free rental scanner at the auto parts store cannot read. Chassis trouble code C0327 indicates a fault with the encoder motor sensor, which is consistent with your symptoms, and is also typical of your model year and drivetrain. My 2005 6.0 had the same trouble code, and a new sensor fixed it.

 

As for OnStar, unlike previous model years, the 2005 model years have dual system (digital/analog) telematics equipment that remains compatible with the current digital only OnStar service. If your new to you truck is thus equipped, and you were thinking of subscribing anyway, then that subscription will solve your proprietary trouble code scanning issue to diagnose the problem you are having.

 

While the fault is highly likely to be the encoder motor sensor, it is not always. In earlier years, it was the switch, although by 2004/5 people who were replacing switches found that they were really just throwing parts at the problem based on what worked in previous years, and the problem recurred again until they scanned the truck to find out what the real problem was. If the Service 4WD message light came on, then a code was set. Get that code before paying for parts to be thrown at it.

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