Door Lock and Unlock Operation

The BCM PWR fuse supplies battery positive voltage to the BCM for the door lock system.

The BCM supplies and monitors a reference voltage to the door lock switch through the door lock switch lock/unlock signal circuit. The door lock switch also receives a constant ground source. If a door lock switch is placed in the lock position, the reference voltage is taken directly to ground and the BCM senses 0.0 volts on the signal circuit. If a door lock switch is placed in the unlock position, the reference voltage is taken to ground through a 15k ohm resister that is internal to the door lock switches and senses approximately 2.9 volts on the signal circuit. This is how the BCM determines what portion of the door lock switch was activated.

The BCM, upon receipt of a door lock switch lock or unlock signal, will switch the appropriate door lock actuator control circuits to battery positive voltage. The opposing side of the door lock actuators are connected to ground internally within the BCM through the other door lock actuator control circuit and the doors will lock or unlock appropriately.

Vehicles without keyless entry have two internal drivers in the BCM to control the door lock actuators. All door lock and all door unlock. Vehicles equipped with keyless entry have three internal drivers in the BCM. Driver door unlock, passenger door unlock and all door lock. This is done to isolate the driver door lock actuator so it can be unlocked by itself using the keyless entry transmitter.