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Discussion Starter · #1 · (Edited)
I started driving my wife's 2008 Cobalt LT to work so we could save miles on our newer car. It sat for about the last 2 years since she was working from home. It is at 120k miles. Today after I picked up lunch it wouldn't start, no attempts at cranking the car. Dash lights up, radio is fine. This happened once before to me after work... I removed the key, waited a few seconds and then it was fine. Happened once and then no issues for over a week since then. She tells me this had happened to her every so often and she did the same, just took the key out waited a few seconds and then was fine.

So I go to Advanced Auto in the shopping plaza and the guy brings out his tester. We see the battery is pretty old, a little low on charge but still had almost 400 cca/590 cca which is enough to at least try to turn the starter. The ground terminal is pretty corroded too and the trunk had some water in the well. We try with a jump pack and it doesn't change, still no attempts to crank. I started doing some research and find the BCM issues with this car and how it controls the starter. I'm betting this is the same problem for me.

It did have some CEL, a few for the rear o2 sensor circuit voltage low/stuck lean, and then P2176 for Throttle Actuator A Control System Idle Position Not Learned

I'm wondering the best way to go about this and what is stopping it from cranking.
I pulled the 50A fuse in the trunk and the fuse ends and socket had some light white corrosion. I couldn't see a crack but I've had other cars where there was a hairline one. I cleaned the fuse with a stainless scrubby and it sparked when I put it back in the socket. I didn't have anything to clean the fuse holder though.

Should I just unhook all the connectors on the BCM, clean and grease them and reseat on module?
What are the chances of the fuse box being the issue? Since broken/cracked/corroded boards seem to be common culprit also. I just can't believe it'd be the fuse box after running just 2 minutes prior to picking up the lunch order.

The car is in a parking lot about half an hour from me right now, so I'd like to avoid having to tow it home if I can fix it.
Or at least "jump start" it somehow bypassing the starter controls and drive it back to work on in my garage.
I have tools and multimeter I can bring with me. I'm used to working on cars just haven't done much work on hers so no idea where some of this stuff is under the hood and honestly really hate electrical issues like this.

Can I jump the BCM/Starter Relay and just force the starter somehow?

Any help is greatly appreciated.

I just wanted to add I haven't seen other random electrical issues. Her gauges have been accurate, radio has been fine, turn signals, A/C etc, have all seemed to work fine the last few weeks I've driven it.
The security light looks like it is on on the dash. She doesn't have any power anything I don't think the key has a transponder in it.
 

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We had a non start issue on our '08. Everything else worked fine. We had a dead cell in the battery and the security light stayed on- no start- until I charged the battery. After charging we found the dead cell and a new battery fixed it for good. The computer needs a solid 12 volts so go ahead and clean all the battery connections. A little baking soda in soapy water does wonders to remove corrosion. A small paint brush or old toothbrush get into tiny crevices. Clean your terminals, charge the battery and see if that helps. Once the electrics are solid then see if the ignition switch is bad. Track down the ignition relay on the fuse/relay board and rig a jumper. When it happens, jump it, if it works then the ignition switch or relay is suspect.
 

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Discussion Starter · #3 ·
So I bought a new fuse because I saw fuzzy corrosion up both leads inside, cleaned the inline holder with baking soda, water and a toothbrush and some stuff dissolved. I pulled one of the crank relays in the fuse box on the right side I saw in a video for this issue and it had a little bit of corrosion on the bottom right leg, so cleaned that also along with the positive post. I didn't check the ignition switch relay though. I let the battery charge over night at home and also wire brushed the ground cable best I could. Reinstalled it all and it still won't crank. The security light stayed on for only a few seconds so it shouldn't be in theft deterrent mode.

I have a new ground cable showing up Saturday, and the only other thing I saw to try was reseat and dielectric grease the BCM connections and check the fuses there. I kind of feel dumb forgetting that today, but was frustrated that stuff didn't work and it was very hot and humid working in the parking lot! New ground cable shows up Saturday anyways so I'll check the fuses when I do that. I don't want to spend time out there with a multimeter, so if that doesn't work I'll tow it home and this thread will continue!

Really hoping that it is not a BCM or fuse box replacement but kind of looks like it right now. Thanks for the help and direction.
 

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I agree it is too damn hot to be fudging with stuff like this. But the multimeter is your friend. Do you have access to a spare battery and jumper cables? You can take a jumper and rig it to your battery cable at the starter. Put the ignition in "RUN" and jump start the starter. You may get lucky and it will start so you can get it home.
 

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Plan on a new battery soon…or sooner. A little low voltage at the BCM will upset your cobalt big time and point out many of the weak connections. Cleaning the connectors on the BCM is not a bad thing but it’s not a miracle cure for low voltage from the battery.
 

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Discussion Starter · #6 ·
Got the car towed home, guy was fantastic and dropped it right in my garage!
I took the battery out and used old school 2 Amp trickle charger overnight. In the morning it registered 12.7v on the multimeter, so that tests out OK despite its age. New ground cable installed also, no change.

Checked all fuses in BCM and under hood, none looked bad or even questionable. Repeated big bcm connector, there was no corrosion on the box.
Cleaned the ground cable near the starter, it was fairly corroded and is for the starter relay and the engine, still nothing.

When trying to crank you hear clicking in the fuse box. So my friend says to tap the starter, but when we looked at it you could tell it was very corroded and rusty. Took starter out and went to advanced and it would not spin on their bench at all. I've never had a starter just die suddenly on me, but that looks to be the issue and it really is disgustingly green and rusted.

Ordered a used oem starter with 47k miles on it so I'll update when that comes in and hope it fixes it!

Going to work on her front suspension while I wait... doing tie rods, sway bar links, and lower control arm and ball joint. Might just do strut too since it makes a lot of noise and is fairly rusty too 🤦‍♂️ she never really washed this thing!
 

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When trying to crank you hear clicking in the fuse box. So my friend says to tap the starter, but when we looked at it you could tell it was very corroded and rusty. Took starter out and went to advanced and it would not spin on their bench at all. I've never had a starter just die suddenly on me, but that looks to be the issue and it really is disgustingly green and rusted.
I'd say you found your problem!
 
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