Trunk release and door locks

[sunchas]

The trunk release on the keyless entry fob as well as the release button inside the glove box has stopped working on my 2001 Grand Prix SE. At the same time the door locks no longer automatically lock when the car is shifted from Park. All related fuses check out. Could this be a body control module problem? Any troubleshooting ideas? Strangly enough when the car is stopped and shifted into Park the doors lock.

[BNaylor]

Welcome to AF.

Could be the BCM but I'd check other things first before calling it. Are your backup lamps working? Check the fuse marked B/U LP (10 amp) in the engine compartment fuse box. Also, check for 12 volts at one side of the fuse socket. The trunk release relay and release solenoid actuator get 12 volts from that fuse through the transmission range switch (PRND321).

[sunchas]

Backup lights work. Can't help but think that the door locks and trunk release problem are related.

[BNaylor]

Oh they are related. Two common points according to the FSM wiring diagrams would be the BCM (internal) or the trunk release relay not energizing or loaded the circuits down. To split the baby check the trunk release relay at contact C2 for a low/ground when the trunk release button on the remote is pressed. Also, you may be able to hear or feel the relay if it energizes. The relay should be located by the BCM module which is under the left hand side of the dash. Remove the left side cover and/or the kickpanel and you should see it or able to access it. If low is present the release relay is bad. If low is missing then the BCM is suspect. Also, it would be a good idea to remove and reseat the electrical connectors to the BCM module.

[sunchas]

Thanks for all the help. Could you tell me how to test the relay for the ground condition. I know how to use a multimeter, but with todays car electronics I'm afraid of shorting something and making matters worse.

[BNaylor]

First thing is locate the relay. It is a plug-in type. Remove the relay. On the relay will be a diagram. Diagram will show the relay coil contacts and contacts of the switch part. Pins 85 and 86 of the relay are typically the coil contacts and pins 87 and 30 the switch contacts. At the relay socket will be contacts A1 and C2. A1 will have 12 volts from the B/U fuse and C2 will be the low/ground from the BCM module when trunk release is pressed on the remote. So either pin 85 or 86 will coincide with contacts A1 and C2. Make measurements with DMM at those pins socket side. Also, you can ohm out the relay coil contacts to make sure the resistance is correct. Reading should be around 92 ohms. Pins C1 and A2 at the socket coincide with the relay switch contacts......pins 87 and 30.

When the relay energizes all it does in pass 12 volts to the trunk release solenoid to pop open the trunk lid. The other side of the trunk release solenoid is grounded at all times.