To diagnose a bad liftgate lock cylinder, a technician will attempt to insert and turn the key. If the key is difficult to insert or does not turn freely, the technician may try to lubricate the cylinder and get it to free up. If this is not possible, the technician may remove the interior trim panel on the liftgate to access the cylinder, the lock and latch assembly, and the connecting linkage (cables and rods). The goal is to rule out any other components as the cause of the problem. The lock cylinder may be disconnected from the linkage to observe how it operates on its own. If the rest of the system is operating properly, the lock cylinder is replaced.

To replace a liftgate lock cylinder, 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 cylinder is disconnected from its linkage. A retaining clip is unseated and the lock cylinder is pulled from the outside. A new lock cylinder needs to be "coded" by the dealer to fit the key before it is installed.

It is easy to neglect the lock cylinders on a vehicle, especially the one in the liftgate. Should the battery die, a key is the only way to unlock the vehicle. RepairPal recommends that the lock cylinders, whether in the liftgate or in the doors, be operated with the key periodically as part of routine vehicle maintenance. This will help to prevent the cylinders from seizing up and failing prematurely.

A lock cylinder that seems to be faulty should not be ignored. If the symptoms are related instead to a faulty lock and latch mechanism, repairs could be much more complex.

The lock cylinder inside the liftgate on some vehicles is difficult to access. The interior trim panel may also be tricky to remove without breaking fasteners or mounting flanges. In many cases, the repair can be done by someone with intermediate DIY experience. However, the procedure is often performed "blind," as the technician cannot see inside the liftgate to identify the components. Instead it is necessary to work by feel alone or with the aid of mirrors and a good repair procedure source, such as an online manual.