Power locks not functioning

Tiny
JESMAN85
  • MEMBER
  • 2003 PONTIAC MONTANA
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
My original issue was that my power locks would (randomly) stay in a constant state of locking. Sometimes, even just trying to get into the van is difficult because immediately as I hit the unlock on the remote, it automatically locks itself back. I would have to time it perfectly to get the door open. Then, driving down the road, it just continues to lock, lock, lock, lock. I turned off all auto locking mechanisms (i.E. Putting into drive and it auto locks) but it still does this. Again, this is random making it near impossible to test any wires during malfunction.

I looked up some information on how to fix this and in trying to figure it out, I happened upon finding that my power lock button in the vehicle doesn't work. I've had the vehicle for about 8 months and just never noticed. But, thinking the two issues may be related, I started investigating and researching. I've pulled up the passenger side foot plate section and found the blue and white splices for the locks. Everything looked good, but I re-soldered both just in case. I tested with a meter and both are receiving 12V. The wires drop voltage when unlock is pressed, but nothing when the lock button is pressed.

I also looked at the BCM. I tested the nodes from the BCM and both are putting out 12V. I even ran a little test by running a wire from the white wire in the carriage to the blue wires at the splice and when I pressed the lock button, it unlocked the doors. I thought at the very least, this proves that the actual lock button itself functions? Otherwise, I am at a loss at this point.
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Saturday, May 30th, 2020 AT 8:22 PM

5 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,553 POSTS
Hello,

This does sound like the BCM is out but to be sure lets do a CAN scan which is the future of automotive repair you can get a CAN scanner from Amazon for about $50.00. here is a video to show you how:

https://youtu.be/InIlnsjOVFA

Here is the door lock wiring so you can see how the system works with instructions in the diagrams below on how to replace the BCM. Check out the diagrams (below). Please let us know what happens.

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Monday, June 1st, 2020 AT 11:47 AM
Tiny
JESMAN85
  • MEMBER
  • 3 POSTS
So, this could be the BCM even if it's supplying power to the door lock? I ordered a CAN scanner. It will be here on Thursday (June 4th). I'll let you know what I find. Thank you!
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Monday, June 1st, 2020 AT 8:51 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,553 POSTS
Yes, the BCM controls the door lock operation it sounds like the driver is going bad which is common. Please let us know what you find. We are interested to see what it is.
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Tuesday, June 2nd, 2020 AT 1:52 PM
Tiny
JESMAN85
  • MEMBER
  • 3 POSTS
I bought an Autel AL319 to scan my vehicle. It only gave two error codes-one for the thermostat and one for the 02 sensor. But, nothing regarding the BCM.
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Friday, June 5th, 2020 AT 10:42 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,553 POSTS
Yep, sometimes the BCM will not have a code but will still be bad especially when it is an intermittent problem. Does that scanner do a CAN scan?
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Saturday, June 6th, 2020 AT 11:03 AM

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