Mercedes-Benz GL550 Liftgate Lock Actuator Replacement Cost

If a car, van, or SUV has a liftgate, then it probably has an electric lock. Or more accurately, an electrically-actuated lock. The key can be used to manually lock and unlock the liftgate. But if the remote key fob or a switch inside the vehicle is to be used instead, something else has to turn the lock. The liftgate lock actuator is a solenoid (or, in some cases, a DC motor) that responds to an electrical signal and moves to work the lock mechanism.

When a button is pressed on the key fob (or in the vehicle), a signal is sent to the Body Control Module (BCM) which, in turn, communicates with the liftgate lock actuator. The lock actuator is mounted, in some cases, between the lock cylinder and the lock and latch assembly. It is attached to the lock linkage (a cable or rod) inside the liftgate and responds to the signal from the BCM to move the linkage back and forth, to lock and unlock. Many newer vehicles have the actuator built into the latch assembly.

There are a number of symptoms associated with a failing liftgate lock actuator. If the liftgate fails to lock or unlock at all with the electronic controls, the actuator may be bad. Normally (and depending on the type of actuator) a slight clunking sound or a whirring sound can be heard when the locks are activated. If the sound of the actuator becomes weak, excessively noisy, or it begins to make grinding noises, it could be failing. The lock may also move partially, but not all the way, indicating that it is going bad. Sometimes the lock actuator behaves erratically. If the doors lock and then unlock quickly - or they work intermittently - the lock actuator may be at fault. Each lock, in the doors and in the liftgate, has its own actuator. If one of them begins to work erratically, all of the locks may act in unison, making it difficult to know which actuator is the culprit.

All of the locks in a vehicle are tied into the same central locking system; each component may have an effect on the next. Operation of the whole locking system can be impacted. The problem should be evaluated and repaired as soon as possible by a qualified professional.

The liftgate lock actuator does not have a replacement interval and is not part of routine maintenance. The actuator should last the lifetime of the vehicle. Unfortunately, some actuators do fail prematurely. It is not unheard of for more than one actuator on a vehicle to go bad around the same time.

Diagnosis depends on the year, make, and model of the vehicle. If the locking system is controlled by a Body Control Module, a technician will note whether only the liftgate actuator is showing symptoms, or if all of the locks are faulty. If all of the locks are acting the same - failing to lock/unlock, unlocking intermittently, etc. - the BCM may be at fault. The technician will use a scan tool to read data from the BCM. On some older models with a separate lock controller, a software update may be required. If the BCM/controller is functioning properly, the technician will remove the switch inside the vehicle (if so equipped) and test it with a multimeter to make sure it is operating. If the switch has power and is operational, the technician will use the multimeter to check for voltage at the actuator. If the actuator has power but does not function, or if it functions partially, it will need to be replaced.

To replace a liftgate lock actuator, a technician will need to open the liftgate and remove the interior trim panel. Some electrical components mounted in the liftgate may need to be taken out for access. The lock actuator (or the latch assembly in many cases) is disconnected from its linkage and electrical connector.The retaining fasteners are unscrewed and the actuator or latch is removed and a new one installed.

RepairPal recommends that an OEM replacement part be installed in place of a failed liftgate lock actuator. Many aftermarket actuators have a high failure rate. If the actuator prevents the liftgate from locking, as is often the case, no valuables should be left inside the vehicle. Also, the alarm may sound intermittently while the vehicle is locked, so determining the best course of action to protect the vehicle and avoid draining the battery should be taken.

A failing lock actuator can be a symptom of a larger issue with the central locking system, including problems with the BCM or multiple actuators. A fault with the liftgate actuator can cause problems with all of the actuators.

Depending on the specific year, make, and model of vehicle, replacement of the liftgate actuator can be a challenge. The level of challenge depends on whether the actuator is part of the latch assembly or is a separate unit, and how hard it is to access. Vehicle-specific repair information such as an online manual is helpful. An intermediate DIYer can perform the repair in some cases. But, on some vehicles, diagnosis can be difficult if symptoms are related to an electronic problem rather than a single actuator, and a scan tool will be needed.