GMC Troubleshooting Questions? Ask a Mechanic for Answers
If you have a no crank condition, then this may help:
Ok, you need to list all of the codes from each module, ie ECM U0101, BCM U0100 etc.
This circuit may help.
This is sounding like a BCM or power/ground issue.
I'm in Australia Donnie.
I will look up some more info and come back to you shortly.
Can you check with a voltmeter what voltage you have at the battery, and the ALDL diagnostic connector pins 16 and 5?
I would be more concerned with no ALDL communication than your list above.
Example of things working but no power doesn't make sense.
Mode than likely you have low volts to PIN 16.
Ok, battery and ground at ALDL are ok.
Can you measure resistance across 6 and 14, key out vehicle asleep.
Should read 60 ohms.
Doesn't matter which way.
Across 6 and 14, should be 60 ohms.
Your meter is on the 200 ohm scale, perfect for me.
The meter should read zero with the leads shorted, as a first test, which you should always do.
Now across 6 and 14 should read 60 ohms.
What do you get, 60, 120, or open, or short circuit?
Ok, the high speed bus is ok.
Have you tried another scan tool, or yours in another car?
Also, what accessories are fitted to the vehicle?
I would prefer a GM scan tool myself.
When was the vehicle last driven?
Ok, I'll let you know about anything else that might help.
Good night for now.
I think it would be best to have a vehicle wide scan done with a GM scan tool.
Module presence check is the first thing to do.
If still no communication with a GM scan tool, then the accessory wake up may be missing.
You say it went to limp home mode, which would be 3rd gear, and limited engine speed etc.
I feel I may not be able to help you with this much further.
I can open the question to other techs if you wish, but I recommend that a dealer has all the tools to diagnose this problem, of which I am remote, so difficult for me.
I hope my advice has been of assistance to you.
Do you need any further help?