Power Door Locks Malfunctioning? [Archive] - GrandAmGT.com Forum


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04-13-2004, 03:16 PM
Today I noticed that my door locks aren't working correctly. Pushing down (which usually is just to lock) will do both functions: lock and unlock accordingly. Pushing up, usually to unlock, does nothing. Anybody else ever had this happen? Do I have to replace the switch or what? Both doors are doing it, which makes me worry that some larger underlying electrical glitch is there.

04-13-2004, 07:05 PM
Based on your description I would suspect one of the door lock switches is messed up. You must be getting a constant door UNLOCK signal to the BCM - which after the UNLOCK function occurs the switch input is ignored - it only reacts to switch transitions. However when you activate a LOCK command this overrides the UNLOCK and results in both operations.

This will also add a little to battery draw but likely not enough for you to notice unless vehicle sitting for some time.

Suggest you unplug each switch to figure out which one is the culprit.

It could also be some weird resistive wiring short which is fooling the BCM so don't buy a new switch until you actually find one is bad.

BTW the input voltage to BCM for LOCK command is GROUND signal. The command for UNLOCK is approx 1/2 battery voltage. No command would be open circuit and BCM input would be floating at battery voltage.

If you have a voltmeter and were to measure voltage on connector going into the right hand IP electrical center (cavity B4) doubled WHITE wire (or just measure the voltage of white wire on either door lock switch with everything plugged in since the signals are tied together) you will get a better idea of what is going on since the BCM won't respond to a constant voltage on this input, only a transition.

Can you tell I'm an engineer, lol