u0100 communication problem that my mechanic could not pin point the reason after 2 trials.

That code indicates that the ECM and TCM are not communicating. Most common causes are:

Faulty TCM
TCM harness is open or shorted
TCM circuit poor electrical connection

I don't know what they checked, so it makes things harder for me. Can you ask them to explain what was done?

Thanks! Will call them tomorrow to find out.

I'll look for your reply.

Hi, I just found online a GM warranty document saying that ECM and TCM are warranted for 8 years / 80K miles. My car should still be within the warranty period. Any shop that's authorized to perform warranty work must first prove that it's the TCM fault causing the problem before getting warranty coverage for the TCM replacement work, right?

I just talked to the mechanic. He said that he's checked every wire and they visually looked in good shape, the connectors looked good and tight, and no ground open. He said that the next he plans on doing in sequence are as followed:
1. use a temporary power wire to connect the circuit and stop using the original power wire. If that fixes the problem, then he will replace the power wire for a permanent fix.
2. repeat #1 on the ground wire.
3. replace the connecting pins into the TCM and the ECM.
4. replace the TCM
5. replace the ECM

This is a trial and error approach. If #1 does not work, try #2. If #2 does not work, try #3. He will keep on until he's done #5. When asked what's next if #5 still does not fix the problem. He gave no answer. And he said he's about 50% confident that one of these 5 trials will fix the problem.

What's your opinion? Thanks!

To check the wires, he doesn't have to replace them. He just needs to test them for continuity. That will tell him if there is a problem.

Listen, based on your findings, I would take it to a chevrolet dealer. Your present mechanic will most likely find the problem, but how long will it take?

Thanks for the inputs. I will wait until the check engine light comes on again and take it to the dealer.

Let me know how things work out for you.

The engine check light is on.I tried to scan the the car but the only result i get is the exterior and interior connections but not the engine.And i have to get the code from the engine.Is at the mechanics shop and this is the information i got from him.Can you please help me out

Please post your question here

https://www.2carpros.com/questions/new

Cheers, Ken