Tcm/bcm/power Steering/check Engine - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
Problems and Service Talk about any mechanical problems you are having

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post #1 of 21 (permalink) Old 05-24-2011, 11:22 AM Thread Starter
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Angry Tcm/bcm/power Steering/check Engine

2006 Cobalt, purchased used with 27,000, now at 49,000. Soon after purchase during a hot July, the check engine light came on, Power Steering on the display screen and the trans would jerk until reached 35 mph, or so. After disconnecting the TCM and/or battery over a few weeks, the problem disappeared until the next hot July in 2010. Again cleared up as mysteriously as before. Then in December, reoccurred, power steering issue was worse, and it would not clear as easily or stay cleared. Decided to first try replacing the power steering motor under recall. It made the problem worse. Dealer replaced the TCM because that's what the codes told them to do. Fixed nothing. Car came with a side post battery, which I replaced myself this last winter with another side post (Autozone insisted it should be a top post)/what does that little grey tube do?. Dealer says this is not standard and may be causing the problem, but can't tell me how. But could it be? They apparently didn't notice this during the $300 TCM job. In the meantime the problem disappears for 1-2 weeks at a time after first going 1-2 days with the "little lock warning light/power steering warning" activating, then those warnings and the check engine light, then the check engine light only (which clears the trans and steering issues) then the check engine light disappears on its own. I have read hours of threads on this and other sites and consumer blogs. The dealer claims/feigns ignorance on any of this ("we've never encountered this before"). And I've finally began to notice that when these other problems occur, I have a power/voltage fluctuation - the lights dim and brighten, the fan slows and speeds, the A/C cuts in and out. I'm not anxious to drop another $300 plus to the dealer to replace the BCM since they are just guessing. My question is has anyone ever come up with the cause/solution? I see lots of complaints, but no solution. My fear is that the complainers stop complaining after the problem is fixed, or if they get rid of the car, but they don't report back.
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post #2 of 21 (permalink) Old 08-03-2011, 11:15 AM
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I've had the same issue this july. I took all the plastic covers off my motor to hopefully keep it cooler. So far no issues with what it was doing before. What I can guess is (not a mechanic mind you but I'm and IT guy) The TCM computer must be overheating and going BatSht crazy. Here in Kentucky it's hit over 100 this july and August so far.
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post #3 of 21 (permalink) Old 08-03-2011, 12:27 PM
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I was having problems with my car as well not trans and power steering but head lights and voltage. I threw 300+ dallors at it like you and and it didn't help either. I unhook the battery and took all the conectors off the BCM and the problem have not come back in about 5 months now.
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post #4 of 21 (permalink) Old 08-14-2011, 09:46 PM
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this just happened to me tonight..power steering came on but went off within 1/8th of a mile but kept doing the jerking thing till about 30 mph then when came to a stop it kinda sputtered like it wanted to die and lights dimmed and the t/c light was on..then shut if off checked some things and 10 minutes later its fine..would really like to know what was going on..
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post #5 of 21 (permalink) Old 09-06-2011, 10:30 AM Thread Starter
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For the last 6+ months I had been having troubles with engine warning lights, trans shifting, power steering and A/C cutting out. Replaced power steering motor under recall. Had TCM replaced per the dealer and the diagnostic codes. Didn't fix the problem and dealer was just guessing from that point. Had the ECM "flashed"/codes cleared by a garage guy who has the software. Fixed it for a week. He said if that failed, it was likely the BCM. Didn't want to pay new for BCM, but couldn't find a junked one locally. Apparently Cobalts are too new to be in most junk yards in the Chicago area! Those that admitted having the parts, refused to sell them (too many complaints about mis-matched electrical parts). So out of need to match the serial numbers on my part with what is available on Ebay/other sources, I pulled off the BCM cover - passenger side center column, black cover snaps off. While in there, I pulled the two "computer plug" connections, wiped off and reattached. Pulled the fuses across the top (which just so happened to be in this order: power steering, transmission, A/C and A/C). Wiped the contacts which seemed to have a grease feel to them. Blew out the whole thing with the air hose. Lots of dust - the car's ventilation system blows right past the back side of the BCM. It was clear someone had been in the BCM before I purchased the car used as all the spare fuses had been removed. Reattached everything and (cross your fingers), no problems for almost two months. Knock on wood, I hope this did the trick. I wanted others to know, because this was a frequent post.
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post #6 of 21 (permalink) Old 09-06-2011, 01:49 PM
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Originally Posted by William View Post
what does that little grey tube do?. Dealer says this is not standard and may be causing the problem, but can't tell me how.
LOL The tube is like a vent. in case the battery acid inside heats up and boils over, the tube vents it to outside of the vehicle. Having cups in the cup holder is just as likely as this thing causing the issue.

Hopefully you fixed it, at least until next July. I have a used BCM from an '07 I could sell you cheap. It didn't program for my car, but mine had some serious computer issues. Might work for yours. I've got it posted in the "for sale" sub forum.

Last edited by acoutu; 09-06-2011 at 01:53 PM.
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post #7 of 21 (permalink) Old 10-10-2011, 08:13 PM
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One thing that you may want to try is to disconnect your battery and then touch your positive and negative cable together for about 15 sec. then reconnect battery, what this does it will reset your control modules. might give that a try
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post #8 of 21 (permalink) Old 12-14-2011, 06:35 AM
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same here

I'm having the same problems with my wife's 2007 Cobalt. It's currently at the local GM service dept (day 2) and they seem to have no idea whats going on. Their answer is to replace the BCM but they wont guarantee that will fix it. I'm just a little leary of throwing $$$ at it until they're satisfied and still have the same problem. Has anybody had this problem fixed?
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post #9 of 21 (permalink) Old 12-14-2011, 07:38 AM
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I think there's a GM bulletin on this let me check and I will edit this post with my results.

WOW, not easy to extract from VMware, but got it I think. This is right out of the GM service Manual. You could print and bring it to the technician working on your car. Sometimes just disconnecting and cleaning the 3 connectors on the BCM solves the problem, but sometimes you have to recrimp some of the .64mm pins in the connectors. Dialectric grease also helps prevent corrosion.
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Last edited by Coby7; 12-14-2011 at 08:49 AM.
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post #10 of 21 (permalink) Old 12-14-2011, 08:36 AM
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Heading in

GM service called and said they couldn't figure it out. They've effectively given up. I'll bring the bulletin to them to see if it'll help them. Thanx!
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