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Possible BCM bad

 
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whosonfirst
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2002 Chevrolet Impala


PostPosted: Thu Sep 29, 2011 11:32 pm    Post subject:  Possible BCM bad Reply with quote

My 2002 Impala LS with 103000 miles is having electrical symtoms of the weirdest kind. When the ghost appears the door locks cease to work from park to drive and back to park. The door locks will function with the unlock door button. The RDR radio settings function quits working. The A/C compressor may or may not work. The electric cooling fans may not work and engine overheating may happen if not moving in traffic. I put an after market catalytic converter on the car and get the P0420 code. That is the only code coming up. I use to be able to get rid of the electrical problems by pulling the 10 amp fuse for the cluster/BCM. Now I have to wait for 1 hour for this trick to work after pulling the fuse. After the electrical problems go away they can come back again with car just sitting. I disconnected the Onstar module and still does the same thing. I have the old type Onstar and never upgraded to digital. Thinking positive. These problems are caused by a bad ground. Right? What you say guys? No woman here I assume. I don't have a tech II code reader and hesitate to go to a dealer. If I can't fix it myself than the car is junk to me. I try to fix everything myself. Can't help it.
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2001 Chevrolet Impala
2000 GMC Sierra
2001 Chevrolet S10
1994 Ford Mustang


PostPosted: Fri Sep 30, 2011 1:06 pm    Post subject:   Reply with quote

I'm not able to diagnose all your car's issues myself... all I can ad is that when my BCM was bad, none of those issues were happening to mine. Doesn't mean it may not be bad though. I've read others having weird occurrences that were different from mine when theirs went out. A dealer may not be your only option either. The garage I normally use has the capability to reprogram the mileage when the BCM is replaced, for cheaper than what a dealer will do it for. It's still expensive though either way! Goodluck!

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bbengineer
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2004 Chevrolet Impala
1998 Chevrolet Corvette
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1970 Chevrolet Chevelle


PostPosted: Fri Sep 30, 2011 1:18 pm    Post subject:   Reply with quote

Just an FYI, the mileage isn't stored in the BCM for the 00-05 Impala...

The vehicle options (RPO) and configuration are what need to be programmed into a new BCM (used BCMs aren't programmable at all)

Anyone with a Tech-II can configure/program a BCM, but most shops don't have one... all GM dealers do

BBEngineer

PS: It does sound like the BCM is bad, but you need a Tech-II to confirm. The P0420 code isn't due to the BCM, it is likely due to the fact you replaced the cat with a non-OEM one which will typically trigger that code

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REDLINE
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2001 Chevrolet Impala
2000 GMC Sierra
2001 Chevrolet S10
1994 Ford Mustang


PostPosted: Fri Sep 30, 2011 4:35 pm    Post subject:   Reply with quote

Yep, thank you, I didn't really completely state all that.

I was not, however, aware used BCMs weren't programmable at all, huh.
How/why do people sell those then I wonder?

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whosonfirst
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PostPosted: Fri Sep 30, 2011 6:32 pm    Post subject:  Strange electrical symptoms on my 02 Impala Reply with quote

I thank you both for the reply. It is like a jig saw puzzle and I am putting the pieces together to figure out what is causing the strange symptoms. I have installed an after market coolant temp sensor from Auto Zone a couple years ago. I had my trans cover off and replaced the 4th hub and clutch assembly and updated some valves. I replaced all the trans solenoids and sensors. I was thinking that if the trans sensors communicate with the BCM to tell the BCM if it is in park or drive that maybe the sensor is giving the BCM a bad message like sending info that the trans is in both park and drive. How would the BCM logic handle that message? Maybe it would get stuck in a closed logic loop. I could disconnect the grey valve body electric plug on the left wheel well and see if any different results happen. Any thoughts on that?
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1998 Chevrolet Corvette
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1970 Chevrolet Chevelle


PostPosted: Fri Sep 30, 2011 6:39 pm    Post subject:   Reply with quote

The BCM doesn't read the transmission, the PCM does

BBEngineer

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whosonfirst
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PostPosted: Fri Sep 30, 2011 10:42 pm    Post subject:  How does the BCM know to open and close the door locks? Reply with quote

I first noticed the problem when the door locks did not unlock when put in park. At times the door locks don't lock when put in drive and at times the door locks don't unlock when put in park. At times the radio settings menu won't scroll or settings will not come up after holding the lower big knob in for 10 to 15 seconds. The A/C works but sometimes it didn't. How does the BCM know when the trans is in park or gear? I replaced a selector switch in the trans when replacing the 4th hub and clutch. If that trans gear sensor talks to the PCM then the PCM must talk to the BCM. I don't have a wiring diagram or any info on the wiring. Thanks for any info.
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whosonfirst
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PostPosted: Sat Oct 01, 2011 11:26 am    Post subject:  Adding another piece of data Reply with quote

I just noticed that my backup lights sometimes don't work and sometimes they work and won't turn off. I can hear the relay click on the passenger side when they turn on and off. The door locks and backup lights seem to malfunction independently from each other. The door locks might lock in reverse but the backup lights might not come on or vise versa. The backup lights may be on while driving down the road in drive. The backup lights can be on in park and won't shut off till key is turned off. Maybe the BCM is doing this?
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