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This post is for anyone having what appears to be the common and frustrating Cobalt issue of no crank.

My issue turned out being a bade brake module AND a bad fuse box.

This turned out being a nightmare for me and I searched all the forums and found the standard reply "probably a ground" which wasn't bad advice but did not fixed my problem. I hope this post can help anyone in the future save some time and avoid the pitfalls I went through.

2 Recommended links to start:

I recommend doing the DLC quick-tests first, if i had followed this it would have saved me a lot of time. The tests are detailed in the video.


This also covers the issue and is a great place to start:

Chevrolet Cobalt No Start — Ricks Free Auto Repair Advice

Here's a brief overview of what happened with me... no crank out of nowhere, car ran fine. Scan tool was unable to connect at DLC. If you cannot connect i recommend the DLC quick test youtube link above. I had good power and ground, but i did not have 60ohms across pins 6 and 14. This could mean a couple different things but likely a bad module. Here is where I got lucky, I pulled on the harness under the ECM and the brake module motor activated. I assumed the module was faulty and replaced. This fixed my Ohms issue (I was reading 8 ohms and after replacing module i was reading 60 as it should) but the car still would not start even tho a scan tool would connect. So with the CANBUS system now in good health I'm back to square one. I decided to check the fuse box after talking to a mechanic friend. Sure enough I found a cracked circuit board, got a replacement from a junkyard and victory, the car started right up.

Also, something that bugged me that ended up being nothing was that the security lock light would come on when i turned the key on trying to start. This side tracked me into thinking i might have a security issue, bad key...etc... this had nothing to do with my issue.

This problem can really suck, keep after it and it can be solved. I hope these links and story will help someone else in the future. Good luck.
 

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GMs of this era seem to have fuse boxes that go bad. I have had a number of Cobalts, Impalas, and Silverados have burned or corroded connectors in the fuse box. Sometimes have had to run new wiring when a harness gets damaged, most people don’t want to pay for a whole wiring harness. It’s been a while since I’ve had a Cobalt come in with a bad fuse box.

Most of the time if the data link connector is dead, it’s usually two things. A bad fuse, usually the cigarette lighter socket circuit. Or a bad module. Usually bad PCM, but not always. Newer cars are becoming more saturated with modules making them harder to fix when things go wrong. I’ve seen several cars go to the junkyard because the electrical repairs over run the vehicles value. Chrysler products especially notable.
 
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