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Discussion Starter #1
I have a 2002 3.4L Impala with weird electrical issues .

A few years ago , it exhibited Passlock symptoms , would not crank , wait ten minutes or so and would be fine . As it was very intermittent , I didn't do anything .

Since the last 6 months :

Has had no start , security light on when driving issue more often .

Radio would not shut off after shutoff and door opened , would not respond to any commands , or key cycling . Removed and reinstalled fuse to shut it off . Did this once , hasn't since .

One day after starting car , trunk release cycled repeatedly until I disconnected servo in trunk . Reconnected the next day and wasn't doing it any more , but every once in a while it just goes off and I have to stop and close the trunk .

Now , the battery discharges overnight . It's a known good almost new quality battery , and the car's charging system is good . If I disconnect the battery it doesn't discharge . I put it on a battery charger to bring it back up .
I haven't used a multimeter yet to check amperage draw , but it is my understanding that after a while , the car should be drawing about 30 milliamps max . By "eye judging" the spark when touching the negative post with the cable , it's much more than that .

Until I get a proper ammeter , I have the BCM and radio fuse out , to see if that makes a difference .

Several questions :

Should I start with the BCM , or passlock sensor ?
Given the oddity of my other issues , I would lean towards the BCM , but if it's the passlock , can it be replaced without the whole freaking assembly ?

I know I need to determine where the power draw is , but has anyone ever heard of the BCM causing it ?

When determining power draw , should I start with the fuses in the engine compartment on the passenger side? I.e. the big 60 amp ones ?

Also , should I suspect the actual ignition switch ?

If I replace the BCM , my options are about 95 for a reman , 190 for delco .
To program it to my car , do some repair shops other than the dealership have the Tech II device ?

Thanks in advance for any input . If someone's got a wiring diagram for this car , I'd love to obtain it .
 

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I eat brains... gimme brains!
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658 Posts
Check your alternator 1st... a lot of shops only check it when the car starts, but they need to get another reading while its hot.. you could have a bad alternator

Ignition switch sounds to be a culprit, but there is no testing those..

PCM should be purchased by Overkill.com... any remanufactured pcm is bad news
 

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Discussion Starter #3
Check your alternator 1st... a lot of shops only check it when the car starts, but they need to get another reading while its hot.. you could have a bad alternator

Ignition switch sounds to be a culprit, but there is no testing those..

PCM should be purchased by Overkill.com... any remanufactured pcm is bad news

I am reasonably certain (although will again test with multimeter when I get it) that the alternator is ok , because even with a low battery , once the car starts , everything works and the car is fine . It will operate normally and will restart immediately after driving it . It just brings the battery down overnight .
Maybe there's a fuse for the keyswitch . I'll have to look again tomorrow morning when I try the car after reinstalling the BCM and radio fuses .

Not sure about the overkill.com link . Saw nothing there related to a BCM .
 

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Mr. Handy
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6,289 Posts
Sounds like a failing ignition switch and not the bcm.
 

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I have a very similar problem with my 2000 Potiac Grad Am GT1 3400 motor. In my case I believe the lights come after my daughter leaves the vehicle which in turn drains the battery. My temporary solution has been to install a battery disconnect at the battery. This is a real pain in the arse but it was a temporary fix until the springtime. To fellow IF members please help those of us with this problem. Thanks in advance.
 

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8th Gen Antagonist
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Drop your drawers and get ready for a moon spanking! Definitely sounds like a BCM problem. The reason the battery dies is because the BCM keeps turning things on all night, common problem. There may be some shops out there with a tech 2, but it can be hit or miss, and I don't know if they have the knowledge to program a BCM or not anyway.
 

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Mr. Handy
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^^ Most bcm failures are caused by the ignition. And alot of times what you think is the bcm messing up actually ends up being the ignition. I have read numerous cases of people replacing the bcm and a week later its dead again b/c the ignition took it out.


When replacing a BCM I believe only DEALERS can program/set them up.
 

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8th Gen Antagonist
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I have only had one BCM replaced before, and I replaced the ignition switch in that car about a week prior because I thought it was the problem. I suppose it makes some sense that the switch could have caused the BCM failure though...
 
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