2002 Chevy Monte Carlo, Electrical System Problems

by Bruce Kunz
(Granite City, IL USA)

It started a few months ago when I noticed my remote keyless entry wasn't working. I checked the remote and the battery was okay. Shortly thereafter, I had warning lights on the dash indicating three messages: 'service vehicle soon' 'security' and a red battery symbol. These three messages would cycle one after the other. When they appear (and it is intermittent, about half the time) the radio (sometimes) locks up; the a/c quits blowing cold air (the blower works and the indicator light, but the compressor doesn't work); the trunk pops open on its own; the power door locks cycle in and out (sometimes); the auto headlight control quits working and you have to turn the lights on manually; the cruise control quits working... and I guess that's about it! These symptoms sometimes occur randomly and not all at the same time. The only common denominator seems to be the warning lights coming on. I sometimes start my car in the morning to go to work and it "MAY" run to work before it starts acting up, or it may run okay to and from work. It might work for a day or two and then all of a sudden it starts acting up.

I've had a lot of advice... parts store guys, auto mechanics, etc. I've been told it could be the body control module or the ignition switch, which is a $150.00 part. That's all well and good, but I'm told I may replace the switch, which is what MOST people say it is, only to find out that the BCM is bad afterall... OR also. And electrical parts are non-returnable. Very frustrating.

If you can solve this problem, I'll be more than happy to recommend your site in my weekly old car story on my website.

Thanks!

Steve Says,

Thanks for asking me your question. The most likely cause of your problem, is the BCM. BUT the first things to have checked (you can have this done for free at most auto parts stores) are your battery and alternator as well as your battery cable connections. Be sure that the connections are clean and tight and then have a load test done on the battery and alternator. It is unlikely that these are the problem, but it is possible.

These cars have had HUGE problems with BCM's. If you decide to replace it you will need to get it from the dealer and have them program it for your car. You can find them at used parts places but I recommend getting one from the dealer because it is very easy to buy used ones that are bad or that will go bad soon. This part should be in the $300 range plus the labor for reprogramming it at the dealer.

If you want to check this out further you can check the connectors to the body control module. Make sure they are tight and check to see if they have been probed. If someone has probed and pulled on them then your problems could be caused by that. This is unlikely, but something worth checking out. If you are more mechanically inclined or if you want your mechanic to check this out, then you can check to see if there are any voltage drops on the power or ground circuits to the BCM. Any good mechanic will know how to do this.

I hope this has helped. If you have follow up questions you can comment on this post and I will answer when I get a chance. Also, if you want to do more testing on the BCM and want more professional advice, wiring diagrams, step by step repair procedures, etc. simply type your question into the box below: