Intermittent door locks

[Jminuteman]

I have a 2008 Grand Prix and trying to find out what is causing all 4 door locks to work intermittently either with the key fob or inside door switches. The doors would lock when you start driving. It seams like the hotter the air temp is the worse they work. Some days three may not lock but driver door wil lock then other days the driver door ad rear passenger door will lock but not the other ones. Today the air temp is 89 degrees and none of the doors will lock or unlock. When it was new it was random and dealer said nothing was wrong the the locks since there is no trouble codes. Could it be the Body Control Module? Also, the passenger air bag is intermittently and goes off and on at times. Dealer indicated no trouble code, no problem. Any help is appreciated. 

[Frosty]

There are several possibilities, the challenge will be figuring out what the cause is. I will start from easiest to more complicated/expensive.

1. Check your power door lock fuse. I know you said things work intermittently but if the fuse is contaminated or compromised in some way, it probably warrants replacing regardless. Your owners manual should be able to tell you which one it is.

2. Pop out the main contract switch panel from the driver's side door - most usually require a flat blade screwdriver. Look at the connector underneath the switch panel. Do you see any loose or corroded connections. Are there any broken wires? Reconnect everything, make sure the connections are snug and tight. Perhaps use a little di-electric grease on the connectors too. Test the switches and locks (all of them) before putting it back in the door panel.

3. Disassembly a door panel other than the driver's door- say the left rear door. Find the connector to the power door lock. This is probably a 6 pin connector but only five are used. If you have a power probe or another 12V source, apply 12V to pins 2 & 3 (unlock and lock). That should test if the lock actuator works. If it fails, then the motor inside the assembly is bad. The cover is held on by a couple of rivets that you can carefully drill out and tap for 8-32 screw. Inside the motor has a small gear.

So you may need replacement locks. A set of replacement door lock actuators from the dealership may run around $200 or more for a set of four. Test all the doors and determine how many locks you really need.

Again, as above - check the state of the electrical connections as well.

4. Lastly, replace the BCM (Body Control Module). Most expensive option..

 

If I was a betting man, I'd say your problem is somewhere with either #2 or #3. BCM's can fail, but I sort of doubt it because I'd expect you to experiencing other issues with the car too.