2006 Chevrolet Cobalt - Electrical gremlins are taking over

My 06 Cobalt power steering light on the dash stays on. The door locks start locking and unlocking. The speedometer, gas gauge and tachometer only work intermittently. When they aren’t working, the transmission doesn’t shift properly. The first time it happened, I unhooked the battery for 24 hours and when I reconnected it, the car was perfect for about 3 weeks after the reset. Now when I try to reset the computer, it doesn’t change.

How long have you owned this car?
Has it ever been in a flood?

I was tempted to state that the problem is most likely the result of a bad BCM, but when I read that you also have transmission problems, I think that flood damage to most of the electrical/electronic components is the most likely explanation.


+1 to flood damage, I also wonder about the state of the electrical system as well. If the battery isn’t holding adequate charge and/or the alternator is functioning properly, it could be causing all sorts of electrical gremlins.

More than likely the BCM is failing.

The BCM is the “gate keeper” module on many 2003 and newer vehicles that have a CAN (Controller Area Network) system. If the BCM cannot communicate properly with all of the other modules, or it does not recognize the addresses of other modules, it can cause all kinds of problems.

This includes the transmission control module.


There are no signs of flood damage.
So far, the BCM looks like the most likely problem.

There are no signs of any flood damage.

Yes, but…
Have you owned this car since it was new?
If not, then it could have been in a flood before you bought it.
How long have you owned it?

In any event, if there is no damage from flooding, then my original impression–of a bad BCM–is probably the source of your problems.

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We bought the car 7 months ago. I can’t find any signs of of flood damage under the carpet or under the rocker panels. The car ran perfectly until a month ago. I reset the CPU by disconnecting the battery for a day and a half. When I reconnected the battery, it worked perfectly for more than 3 weeks. But now it won’t reset again.

How old is your car battery? I know sometime weird things happen when a car battery is on the way out, due to low voltage, etc.

Additionally, a failing alternator can produce voltage “ripples” that electronic devices do not like.

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I expect the problem is the battery/charging system. But good idea to test it b/c it could be that system, and the test is fairly easy for a shop (or you if you know how to use a DVM) to do. This presumes you are able to start the engine.

Let car sit overnight. First thing in the morning, before starting the engine, the battery should measure about 12.6 volts. Immediately after starting the engine, 13.5 - 15.5 volts. What do you measure.

I load tested the battery and it tests good, but I will will check the alternator with a digital volt/ohms meter.

The battery was brand new when we got the car, and it load tests perfect without having to charge it first.