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I will have to give my personal line to whoever else have this issue to get into detail and show Where the issues may lay. It’s very confusing. But the problem of mine I believe was ground G101 receiving heavy corrosion and going bad in an essence along with my fuse block under the hood receiving heavy damage from the slipped power line. But other known issues are the wire harness resting on the front right of the motor being dug into the sharp corner while adding excessive heat making power wires ground out on the block sending a short there the charge system, and a hook up under the steering wheel on the right of the little cubby hole our trunk button sits in, getting shorted from a sharp metal fragment/ loose wires causing EMU TCM BCM communication issues making your transmission act as if it’s gone threw 500k miles and on its last 50 yards of life. Cobalts we’re electronically made to fail, and it’s safe because I favor my governor regulated LT over my old EJ6 b18b swapped civic.
 

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give me little more details on its condition before it starting. Did you just work car it or treat it like it was a million dollar BMW? there are several reasons I found, and when I dug into all at once plus adding a self powered/forced ground toggled by a toggle switch I resolved everything within the vehicle and have since drove an additional 5200k miles. Most I get is a bog upon heavy braking and I assume it’s from the fuel filter being GM original. I bought a salvaged rebuilt 06 LT coupe with 148k on the cluster. A loose piece of shit battery terminal coming loose caused a power line to slip and touch the vehicle frame still energized and zapped the weakest ground within the vehicle which was fixed and I assumed heavily damaged my fuse block Which has proof of heavy damage. 33 year GM/ ASE certified grandfather helped me fix everything, and I found everything he didn’t understand threw the internet. Which found the way to my cobalt turning over again. Give me symptoms, miles, car condition care to vehicle and state you live in and I’ll help you locate you’re issue
Thanks for the reply.

I purchased the used car about 1.5 years ago, and was driving it about 8 miles a day M-F, was very easy on it. Live in FL. The car, 2006 Cobalt 2.2 coupe has 90,201 miles.

The symptoms:

First issue occurred about 5 months ago. Started vehicle, noticed the power steering warning came on and had no power steering function. Parked, shut the car off for about 5 minutes, car started and was driving fine, like normal.

Next issue about 5 months later: while driving in normal condition power steering message came on but the power steering was still functioning, Transmission shifting jerky seemed to not want to shift, and the air conditioner seemed to not be blowing cold air. Got to a parking lot, shut off, the car started again after about 15 minutes but all the issues were still present. Tried to baby it home. Also noticed en route all the gauges stopped functioning, RPM, Speed, and Fuel all dead. The car died on me en route and it hasn't worked since. Got a tow to my house.

Sitting in my driveway now and I've been picking away at it. Digging through forums etc. Here is what I have done so far.

Cleaned and re-lugged 3 grounds. The grounds - one was directly behind the cooling fan, under the driver side headlight, and under the coolant reservoir. They looked green and I read that solved the issues for others, it did not solve my issue.

Checked all fuses and relays, under hood fuse box and in the passenger side console. All good.

Scan tool unable to communicate. At this point i replaced the ECM. ECM was ordered online and the shop programmed it to my VIN. Install new ECM and performed the 30 minute key relearn procedure. The procedure came with the component I ordered. I followed the procedure and it behaved as described, anti-theft light stayed on for roughly 10 mins, then turn key to "off" without removing it, and do this 3 times. Finished procedure but no luck.

After doing the key relearn when I attempt to start the car the anti-theft signal lights up for about 3 seconds. It seems to have a mind of its own, sometimes lights for 3 seconds, sometimes stays lit over 10 minutes, sometimes doesn't light at all. In all cases no crank. Scan tool is still unable to communicate with new ECU (as well as old). However, after the key re-learn procedure I was able to get my scan tool to communicate one time, the first time after doing key relearn, it connected and said No DTCs present. Now it is back to not being able to connect. The fuel gauge has a mind of its own, it typically will go to the current fuel level for a few seconds, then it falls to empty and bounces around in between.

I think this about covers everything. Issue seems to have come out of nowhere, the car ran fine all the time i've had it until the issues described here. Any input greatly appreciated. Thanks.
 

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fyi. my 2007 g5, twin of the cobalt, g. i did all the grounds in engine bay, added extra ground wire to pcm. but goes wonky every few months to a year....lose commuinication to ecu, fuel needle goes awry, power steering messages etc.
mostly starts and drives but seems to downshift when ever it wants, rpms jump all over the place and becomes undriveable.
solution was to replace 10 amp fuse and/or clean the 10 amp fuse and clean terminals in the fuse panel n fuse box passenger side which is #25 Engine Control Module, Transmission Control Module 10amp fuse.
clean with a fine grit sandpaper even though there were no signs of corrosion in fuse box terminal or fuse. once i do this problem goes away for months at a time but dont forget to recheck the engine bay grounds
 

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fyi. my 2007 g5, twin of the cobalt, g. i did all the grounds in engine bay, added extra ground wire to pcm. but goes wonky every few months to a year....lose commuinication to ecu, fuel needle goes awry, power steering messages etc.
mostly starts and drives but seems to downshift when ever it wants, rpms jump all over the place and becomes undriveable.
solution was to replace 10 amp fuse and/or clean the 10 amp fuse and clean terminals in the fuse panel n fuse box passenger side which is #25 Engine Control Module, Transmission Control Module 10amp fuse.
clean with a fine grit sandpaper even though there were no signs of corrosion in fuse box terminal or fuse. once i do this problem goes away for months at a time but dont forget to recheck the engine bay grounds
thanks for the reply. have replaced all fuses and checked all grounds. I think this has to be a problem with my canbus system because i found when i test ohms across pins 6 and 14 at DLC i read 8 ohms, it should read 60. When i remove the BCM i get 120 ohms so i thought this meant the BCM was bad, got a replacement to check and this is not the issue either. If anyone can give me some thoughts on what it means when testing the DLC I have 8 ohms across 6 and 14 and also 120 ohms across 6 and 14 with BCM unplugged would be helpful. thanks.
 

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its more likely a wiring issue, pin fitment, bad/rusty connections, pita to find. check these 2 vids out on same problem with ohm reading. this guy is a great troubleshooter in car electronics, he uploaded in 2 parts. fyi problem was loose female pins in wiring harnesses. has many vids on wiring problems and the effects it can have in cars



 
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