Wiring can cause door lock problems, but switches and actuators are more common.

DennisB DenLorsTools.com © Summary: A quick common sense way of thinking about and pinpointing the most common door lock problems on many vehicles. There are several things that can cause the power door locks not to work properly. The most common cause of a single door lock not to work, is a bad door lock actuator (also called a door lock solenoid or door lock motor). Another common problem or cause of door locks not working is simply a bad door lock switch. Many cars today have computers that are also in the loop when it comes to controlling the door locks.

Fortunately, body computer systems are pretty dependable and give problems very seldom. It seems as though the most troublesome vehicles regarding door locks related to computer control issues, are Chrysler’s; Dodge Caravan and Chrysler Town & Country vans sometimes have BUS related issues (BUS means “a collection of wires through which data is transmitted from one computer to another”)… but this is still rare. Ford Explorers also have a few BUS issues that can be related to door lock security module, or wiring shorting out that goes from the door into the body. Usually when checked with a scan tool in the body control or security section, there will be a code indicating if there’s a BUS fault.

Problems can also include other failed parts that aren’t high-tech, like a linking rod connector. Sometimes the linkage can pop off during the process of a locksmith using a slim jim or someone using a hanger to unlock a door. It’s easy to hook onto a rod and disconnect a link. In this case it’s just a matter of removing the door panel and maybe adjusting the linkage and replacing the plastic rod retainer if it was weakened or broken.

Door latches can wear, some have the door lock actuators built-in and others don’t, but a worn latch in either case can cause problems. If there is too much play or excess movement, the door lock may not work dependably. When replacing door lock actuators, a lot of times they are only available as an assembly including both the door latch and actuator as a unit. It depends on the make and model how they are which design they have.

Door Lock Diagnostics. First think about the problem logically.

1. If there is only ONE door lock not working, the problem is more than likely isolated within that particular door, barring some unusual wiring issue.

2. If all the door locks work with the passenger side door lock switch, but not the driver’s door lock switch; then the problem is likely the driver’s switch.

3. If a single door lock only works in one direction, either to lock or unlock but not both, then the problem is likely to be the door lock actuator.

4. If ALL door locks work only in one direction, either to lock or unlock but not both, then the problem is likely to be a bad door lock switch.

Question – I have a 2004 Jeep Grand Cherokee and the right rear door lock makes a loud buzzing sound when I try to unlock the door. Can you suggest what the problem could be?

Answer – This is a common symptom of an actuator that has gone bad. It could be the gears inside that are worn not meshing properly, although the exact cause of failure doesn’t really matter since the part is replaced as a unit and not taken apart and repaired.

Question– After replacing an exterior door handle on my Mercury Mountaineer, the door locks will not work properly. The locks worked before, what could be the problem?

Answer – Since the door locks worked before the door handle was replaced, the problem most likely is the link adjustment from the handle to the door lock actuator. If the adjustment is too tight or too loose, it will not work properly. A little free movement of the handle should be felt if the adjustment is correct. It’s best to notice where the positioning is on the threaded part of the rod prior to taking it apart, then check the door lock operation before putting the interior door panel back on.

Question – On my 2003 Ford Explorer, the power door locks go on and off while driving down the road. The door ajar warning comes on the dash and chimes, what could be the problem?

Answer – It’s possible that one of the door ajar switches located in a door latch could be going bad. Another possibility is a wire that goes from the door through the body could be shorting sometimes (see the picture at the top). The Explorer uses a security module located underneath the right rear quarter window behind the trim panel – I’ve heard of cases when the window is not closed, rain can enter and ruin the module causing strange problems due to the water shorting it.