I have a 2007 Chevy Avalanche LTZ. The problem started with all the service lights coming on and saying check everything, suspension, ABS, engine, 4-wheel drive all of it. Also the Dashboard went crazy with all but the battery indicator intermittently jumping from zero to high and no speedometer at all. Radio and Nav work but no back up camera. Transmission shifts very hard from 1st - 2nd. I took it to Advance Auto to put it on the code reader and it wouldn't work just kept saying trying to initialize. Finally took it to a dealer and of course they said they'd never seen this before. They said it shut their TECH II system down also. They disconnect C109 and their Tech II would work. They "narrowed" it down to the PCM, TCM or lines in between for a $200 fee of course. So i drove it this way back from NY to MD because of course I was on VACA when this happened. I drove it one more time and now it won't start at all no click no nothing all the lights and everything works and the Rear compressor for the auto ride shocks will run if I leave the battery connected even with no key in the ignition.

This is what I've checked and done so far.....
1. Check battery and connections all fine battery is less than a year old. Disconnected battery for a full day trying to reset computer didn't work
2. Checked all the grounds that I know of. Under hood, rear frame and side frame
3. Check connections to PCM and TCM and all appear to be fine all look almost brand new
5. checked the wiring between the PCM and TCM and all appear to be ok
4. Check all fuses all are good.
5. Replaced the PCM with a programmed to my VIN PCM and still have the same problem.

My next step is to replace the TCM but I wanted to get some advice before I spend more money that doesn't fix the problem.

PLEASE HELP ME I can't afford to take to dealer to have them tell me it might be this or that for another $200+ bill.

Thanks in advance.

 

You need an experienced shop with the tools and knowledge and equipment to handle this. The problem is probably a high speed databus issue but this is not a problem a beginner should tackle in their driveway. You can spend a fortune replacing modules and not fix it. Ultimately you need a tech 2 and correct schematics and knowledge to try and isolate the problem to a specific area.

You may check the battery cable where it plugs into the bottom of the power distribution center on the drivers side and see if the connector shell is burnt loose or discolored.

 

You could have some mice chewing on wiring. is the alternator working as it should? battery functioning properly?