Good morning, this is my first time posting in this forum. I see this seems to be exclusive for SS models but i really hope to find some answers to my Cobalt problems, which i had a lot almost since day 1... thank you very much in advance for your help. So i own a 2008 LS Cobalt that was giving me a Crankshaft position sensor error code for a long time and the car would shake a little bit from time to time but i really did nothing about it, just had my mecanic replace the sensor but the error code kept showing up. The tachometer stopped working one day and also the car wouldn't start at the first key stroke but once it started it would run fine. A few months later problems came back, this time catalytic converter was so capped that the car wouldn't run at all, i had to turn it off and wait a couple of minutes and then i would barely made it home, so it took it to the mecanic and he had the catalytic converter removed. The day i went to pick up the car, it apparently and for some reason ran out of battery and it didn't start, mecanic connected a battery right to the post next to the fuse box and the car started, but i had the locked car light turned on and also the one with the exclamation mark. The next day the lights were off and the car ran like a dream for about a week. So two weeks ago, I arrived at my job in the morning with no problems at all but in the afternoon when i was about to go home, the car did not start. I had some guys jump starting my car using their truck, but nothing happened. Every light in the car did turn on, so did the radio but the car just wouldn't crank at all! They tried plugging some cable into the post next to the fuse box and even though it did crank, the car did not start. I had the car towed to the same mecanic i've been taking my car to and after 60 bucks, he diagnosed a damaged ECU. I bought an used one, the exact same model (ACDelco 12618031) he said he brought 2 different guys, even a Chevy technician and they were not able to program it, he pretends to charge me $108 just for checking, he is arguing the ECU i bought belonged to a HHR and it won't work with my Cobalt and that i should now buy another ECU. I really don't know what to do now, i have a feeling that if i follow his advice i'll end up spending way too much money. I'm so sorry for the awfully long post but i really need some advices here. Thanks!!

 

 

Based on what you have said I would guess you have a fairly serious electrical problem. Either you have some wires that are crossing or shorting out or your ECU is toast. ECU's do have to be programmed to your VIN number. I used https://www.flashmastersecm.com/ to get a spare ECU and it works fine after doing the security relearn procedure. You could try that and try it yourself instead of forking over cash to your mechanic.

 

1. Remove the relay marked yellow
2. Turn the key to the crank position as if trying to start (nothing will happen but you are telling the PCM to crank)
3. Release the key to the run position
4. Where the relay was, jumper the bottom left socket to the top right. There will be a small spark so don't get frightened and remove the jumper until it starts cranking.
5. If the car cranks and starts, remove the jumper right away.

Anytime you jumper the 2 sockets 30 and 87, you have to turn off the key for a while and start over. You get one try per key cycle.