Door lock actuator: problems, testing, replacement cost

The electronic door lock actuator is the part that latches and locks/ unlocks the door in a car with power locks. In most modern cars, the door lock actuator assembly includes a built-in latch mechanism, as well as the switch (sensor) that monitors if the door is open or closed/locked. The door lock actuator is connected to the inner and outer door handles via cables or mechanical links.

Door lock actuator problems

There are several reasons why a door lock actuator may need to be replaced:
The worn-out door lock actuator can produce a buzzing noise during lock/unlock operation.
The door lock actuator may need to be replaced because it stopped working completely.
If the door lock actuator has failed, it will cause the door lock not to work in one particular door while other door locks will still work. We cut open this door lock actuator in the photo to show you what's inside. If the electric motor or the mechanism inside the door lock actuator wears out, the door lock may lock or unlock slowly or work sometimes, but not all the time. In some cars, a failed door lock actuator may lock but won't unlock or the other way around.

The problem with the built-in switch that monitors if the door is open or closed can cause the "Door Ajar" warning light to stay on even if the door is closed. The same problem can cause the anti-theft alarm to go off randomly. From our experience, many problems with the door open/closed switch are caused by water penetrating inside the door lock actuator and shorting the switch or the pins inside its connector. This explains why the alarm often goes off during or after the rainy weather.

Often, the cable that connects the door lock actuator to the door handle may be built in into the actuator assembly. In this case, if the cable breaks, the door lock actuator assembly may also need to be replaced. See a photo of a broken door lock cable.

If the bolts that hold the door lock actuator come loose, it will cause the door not to lock properly. Bolts holding the door lock actuator must always be checked if there is a problem with the actuator and tightened if loose.

How the door lock actuator is tested

To diagnose, your mechanic may need to take the door cover off, check the door lock linkages and test the voltage at the door lock actuator, following the wire diagram. The voltage is measured when the power lock button is pressed. If there is a voltage, but the actuator doesn't work, the door lock actuator is bad and needs to be replaced.

If there is no voltage present when the power lock switch is operated, the problem must be traced further using the electrical diagram. It could be a main door lock switch, broken door wiring harness, bad connector, failed control module or simply a blown fuse. Read also: how to check a fuse.

Which door lock actuator causes the alarm to go off?

If you suspect that one of the door lock actuators is causing the alarm to go off in rainy weather, the first step is to check the weatherstrips above the door locks. Water can get inside the door lock actuator if the weatherstrip right above it is not sealing properly.

For example, in the photo (click to enlarge) you can see the gap in the weatherstrip which is the easiest way for water to get inside the door lock actuator below. We had one car where the owner fixed the alarm going off on rainy days by sealing these gaps in all the doors and lubricating the door locks and the trunk/tailgate locks.

Check if all the doors close smoothly and the "Door Ajar" light turns off every time the door is closed. If the light sometimes stays on and sometimes turns off when closing one of the doors, the switch in that door is the likely culprit. If any of the door locks look rusted, it's a good idea to lube them with a proper liquid lubricant.

If no obvious fault is found, this problem can be diagnosed at your dealership. In some cars, the mechanic can see which door (or the trunk or the hood) has triggered the alarm for the last several times using the dealership scan tool. If the scan tool shows that multiple alarms were triggered by the same door, the door lock connector and the actuator must be inspected. Often, replacing the affected door lock actuator solves the problem.

Door lock actuator replacement

Replacing a door lock actuator at a dealership may cost 0.8-1.5 hours of labor plus the part that is usually priced within $300 for an average car. Aftermarket parts are cheaper, but they are not available for all cars.

How easy is it to replace a door lock actuator as a DIY project? We would rate it at 6 on a scale from 1 to 10, with 10 being the most difficult. The door cover needs to be removed. The access inside the door is limited and you would need a small flashlight to see inside the door. In some cars, the window regulator together with the window or the outer door handle may also need to be removed, which is often tricky. The most difficult part, though, is to properly connect all the cables and links after the new door lock actuator is installed. You will also need a few clips that hold the door cover as they are easy to break.