Power Locks: Description and Operation

When a door lock switch is activated in the power door lock system, all of the doors lock or unlock in unison. Each lock can also be operated manually from the locking knob. The locks are operated by reversible motors that receive voltage from two relays in the door lock relay assembly. These relays operate to turn the motors ON by applying voltage to one terminal and ground to the other terminal.

When either door lock switch is moved to the LOCK position, it completes the circuit to the coil in the door lock relay assembly. The door lock relay is energized, closing the lock relay. This applies voltage to the door lock motors, which are grounded through the contact for the unlock relay. The motor in each door runs to operate the door locks. When the door lock switch is released the lock relay contact closes to ground again and the motors turn "OFF".

A similar action occurs with the unlock relay when it is energized by either door lock switch closing to the UNLOCK position. The voltage polarity to the motors reverses and the motors run in the opposite direction to unlock the doors.

The door lock switches are usually closed for just a moment. If they are held closed, an electronic circuit breaker in each motor opens to protect against damage. The circuit breakers have Positive Temperature Coefficients (PTC) and reset automatically when voltage is removed from the motor.