GMC Yukon No Communication

Andy.MacFadyen wrote: CAN bus problems are going to become more common and many shops will just throw random parts at them. Everybody here is trying to stay ahead of the learning curve but a lot the shops out there have no chance it took them 10 years plus to learn how to test basic 3 wire alternators.

I don't know if I should start a new thread or just piggyback off of this one but I have a customer that has a 2003 GMC Tukon 1500 Denali and it runs fine but has no communication to the DLC connector. I tested the pins with my DVM and there is no power to any of the pins which it should have on at least to pin 16. I looked at the wiring diagram and it doesn't show much bu. The Cig lighter fuse directly connects through to pin 16 which is okay. This was through Identifix. I just looked on the OEM wiring diagram & it showed a little better.diagram than the regular color wiring diagram has to the connections. I grounded through pins 4 + 6, should I be grounding on battery ground testing power to pin 16 or would that make a difference? Pin 2 has a voltage variation from .23 to 3.7 volts min max. Would it do any good to scope any of the connections? If anyone has any other suggestions on where I should go from here I would greatly appreciate it. Thanks, Doug

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Hey Doug!
I moved your question to your own repair question thread. You'll get much more help this way

If you don't have power on pin 16 of the DLC (and if it's not shorted to ground), I like to jump 12v to pin 16 and see if that restores communication.

Ill part from the assumption that you checked with DMM at the DLC an got no voltage reading.....

1- Pin #6 is NOT a ground, #4 is chassis ground and #5 is sensor ground. .

2-If you got no voltage reading at the DLC it could be either power or ground. If you connect one lead of the DMM - or test light - to pin 16 and the other end to a good ground you will check the power supply; then hooking up to B+ and pin 4 and#5, one at a time, you will check the grounds.

3- This vehicle uses GM(VPW) class 2 comunication, basically it toggles between 7 an 0 volts at pin #2 when sending messages. Your DMM should show a close to 7 volt max reading depending on how fast it is.

4- If the scanner fires up and you still can't communicate with any module then check the com line from pin #2 at the DLC to the splice pack, probably purple/white wire.