Car door lock doesn’t work — diagnose and fix
When you encounter a car door lock doesn’t work condition, it’s important to differentiate between a problem with the latch mechanism and the power door lock actuator. If you can manually unlock the door from either the interior or the exterior door lock cylinder, but the latch won’t allow you to open the door, that’s a problem with the door latch, not the actuator.
Power door lock actuator — what it does
The actuator is part of the power door lock feature.
Using a switch on the door panel or the remote key fob, the actuator is just an electric motor or solenoid that moves the mechanical locking mechanism to allow or prevent the latch from opening.
Door lock actuators wear out
Every time you open your car doors using the remote or the lock/unlock buttons on the door panel, you’re operating the actuators. The repeated use can wear out one or more actuators. In fact, it’s not uncommon for one actuator to fail, followed by all the other door actuators. After all, they all operate the same number of cycles, so they tend to wear out at the same time.
How to test a door lock actuator
The vast majority of door lock actuators have two wires in their electrical connector. When you activate the power door lock system to lock the doors, the system provides battery + voltage on one wire and ground – on the other. When you unlock the doors, the system reverses the polarity, making the actuator work in reverse.
To test each actuator, remover the door trim panel. Disconnect the electrical connector to the actuator. Attach a meter set to DC volts, one probe to each terminal in the wiring harness connector. Activate the lock/unlock switch. You should see battery voltage switch from +12 volts to -12 volts. If so, the switches and power are good and the actuator is bad.
If you don’t see the power switching, get a wiring diagram and check for power at the door lock switches.
Here’s a typical wiring diagram for power door locks
The diagram on the left is for older vehicles where the power door locks used simple relays to toggle +/- voltage to the door lock actuators. The diagram on the right is used in newer vehicles where the door lock functions go through a body control module.
©, 2022 Rick Muscoplat