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Hello everyone! I'm so glad to have found this forum as I just bought a (new to me)used 2010 Cobalt. It's the LT model and I'm having some weird issues. At first when I would drive with the AC on it would cause the car to stall out at some stop lights (i.e the rpms would drop really low and the speedometer would actually jump up tot anywhere between 60 and 100 MPH (the rpms or car would not rev). Then the car proceeds to stall and start right back up. Now it's been a little over two months since I first noticed the issue and with the AC on it will stall every time and even some times with the AC not on. Took it to my local Chevy dealership to run a diagnostics on it to find out the Engine Wiring Harness is shorting out. They gave me a quote of $210 as this isn't covered under the drive train warranty. I'm looking for some help on locating the wring harness to see if this is something I could fix on my own. I've done some research online but don't see much help for this type of car. Any advice would be helpful! Thank you for all the support and for someone putting together this website for beginners like myself!
 

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What is the mileage on the car? I assume it's an automatic.

---------- Post added at 11:43 PM ---------- Previous post was at 11:41 PM ----------

I don't think you have a harness problem

---------- Post added at 11:45 PM ---------- Previous post was at 11:43 PM ----------

I'm betting you have over 50000 miles on the car.

---------- Post added at 11:51 PM ---------- Previous post was at 11:45 PM ----------

My personnal experience is that someone overcharged the A/C unit before selling wanting to make sure you felt cold air before you purchase the car. This makes the A/C compressor really hard to kick start and stalls the engine. Instead of putting $220 dollars on a guessing dealership game, just bring it to an A/C specialist to have them check it out.

---------- Post added at 11:52 PM ---------- Previous post was at 11:51 PM ----------

Cleaning the throttle body won't hurt either.
 

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It has 45K miles on it. I took it to a mechanic on last Wednesday and he cleaned the throttle body controller and that didn't help the issue. He couldn't figure out the problem until diagnostics was ran. It's a 5-speed manual transmission. I've had the air filter replaced and the AC relay as well under the dealers 15 day warranty and that helped the air blow cooler but still stalls. Something I forgot to mention is when the car is stalling on the radio will increase/decrease in volume making me think there is some type of wiring issue. I will definitely take your advise on having the AC checked though. Thanks for the info and any other info you have for me!
 

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Radio get softer and louder may just be alternator regulator kicking in and out because RPM are falling below 600, same with speedo needle. Any spikes in voltage levels will kinda screw-up GMLan communications a bit. So I'm saying your symptoms still point to an overcharged A/C system. Especially if car runs nice without A/C on.

---------- Post added at 08:37 AM ---------- Previous post was at 08:35 AM ----------

Did you check your battery voltage when engine is not running? Should be around 12.3V
 

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Thanks again for the extra info. I'm terrible when it comes to cars so I have no idea what could cause what. That does make sense what you're saying about the alternator though. I haven't checked the volts on the battery but will take it to my local Autozone to have them check it. If it's below that voltage could that mean it's a battery problem then? I've scheduled a visit next week to an AC specialist to have them check the AC as well. I'll keep you posted on what the issue is! Thanks again.
 

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Well if it reads 10.25 with engine not running that means you have a bad cell. It will still start the car, car will still run but it causes havoc with the computers and sensors of the car.
 

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Issue Fixed!

So I just wanted to update that I found the cause to the issue and had it fixed. I took it to an AC shop and they said everything was fine with the AC, then took it to a mechanic friend and he found the root cause. He said the way the wiring was laying on the transmission cause it rub in just a right way on a sharp edge on the transmission and wore down the plastic protective cover and cut into the wires. He replaced the wires that were cut into and re insulated the wiring, also placed the harness in a different location so it has no chance of rubbing against anything. He stated most people won't think to check that as the protective cover is made of really hard plastic that should never corrode and break. He only charged me $75 dollars for it so a lot cheaper than the dealer wanted ($210). Thanks for the help and hopefully this will deter a lot of trouble for someone if they are having this same issue.
 
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