Hi Cobalt Experts!

My son just purchased a 2006 in fabulous condition. Only problem is 2 days after getting it, it either wouldn't start, or it would start but then turned itself off after 3 seconds. A quick scan revealed an ECM error and a recommendation to replace the ECM. We found a second hand ECM and had the same issues. Then we tested the battery thinking it was a voltage issue and that turned out to be fine. Then at one point when it wouldn't even turn over, I locked the door using the key fob twice; first time doors locked, second time the horn beeped, and then unlocked the car via the key fob and it started right up. Every time since then, this seemed to solve the problem except for one time. On that occasion, after locking and unlocking didn't work, I opened the drivers door and then did the double lock followed by the unlock and the car started right up. Coincidence, maybe. Or perhaps maybe the drivers door button is faulty or dirty.

So I am leaning towards an aftermarket alarm that has gone bad although at first glance under the dash, I do not see evidence of such. My second thought is a fault somewhere in the stock immobilizer, if this car has one. Just curious if anyone has been through this before or has any suggestions of how i might fix this gremlin.

Thank you for your help!
Justin

 

I'm pretty sure the 2006 has VATS. It can be disabled in HP Tuners to see if that's the problem. Get your car tuned (good idea anyways) and have them disable VATS. If the car then works fine, you can leave it like that or replace the VATS module and have it turned back on. You'll need to have a key guy (or dealer) program the new VATS module so you can use your keys.

 

Just to close off on this, it turns out that it was a bad ECM. We purchased a used ECM and dealer re-VIN'ed and re-flashed it and the car is running great now.