2021 Mercedes-Benz C300 Sunroof Motor Replacement Cost

Electric sunroofs are fantastic, there is no doubt about that. However, as many owners have found all too clear, they can quickly become a nightmare. If the sunroof motor fails while the sunroof is in the open position, there is little that can be done if the manufacturer did not include a method to close the sunroof manually. The sunroof motor is tucked away under the headliner, attached to the sunroof regulator assembly, and causes the sunroof to open and close when power is directed to the motor. The sunroof motor acts directly upon the sunroof regulator assembly, which holds and moves the sunroof glass and frame. For power sunroofs, the sunroof motor can be thought of as a window regulator motor on the ceiling.

The ability to move the sunroof in two directions is granted by the sunroof motor and sunroof motor switch, which is used by the driver to operate the sunroof. The sunroof motor can have one of several electrical configurations, and these configurations will depend on the type of circuit it uses to reverse directions, as well as the type of external control the sunroof motor will have via sensors and switches. Generally speaking, a sunroof motor will receive power and ground in either wire, depending on which way the switch is pressed. One direction will be the opposite of the other direction. However, there are many variables. A sensor that acknowledges undue resistance while closing the sunroof can alert the body control module to reverse the polarity of the sunroof so it slides backwards. The sunroof position sensor can cause power to the sunroof to immediately cancel, so the sunroof motor cannot move in that direction at all. It is important to understand that older sunroofs work strictly by electrical current from a switch, while modern vehicle's control the sunroof motor by a computerized control module.

A failed sunroof motor will only do one thing - prevent the sunroof from moving. If there is a failure in the sunroof motor, expect the sunroof switch to seem inoperable, and prepare for water intrusion into the vehicle.

Sunroofs that are stuck in the closed position are only as important as the owner decides. They have no impact on drivability, and will not leave the vehicle or occupants stranded. Repair a sunroof motor that left the sunroof closed at will. As for sunroofs that failed in the tilted or open positions, they not only pose a vandalism and theft hazard, they pose the risk of introducing copious amounts of precipitation into the vehicle. In wooded or rural areas, they also leave the vehicle exposed to wildlife and insects. In this condition, if there is no manual option to close the sunroof, it is best to have it repaired immediately to avoid these scenarios.

Sunroof motors for some vehicles, even new models, are known for failure. These vehicles can show signs of failure within a few thousand miles, and are actually considered likely to fail. Most vehicles with a sunroof will likely have an issue with the sunroof assembly or circuit at some point, however that is not only inclusive of the power sunroof motor. Since sunroofs are notoriously lacking in scheduled maintenance, especially in their later years, the regulator assembly and drains tend to cause the most trouble, and the regulator assembly can often require replacement of the entire assembly, including the sunroof motor. This will account for a large amount of power sunroof motor replacement, but many will be the source of failure. Of the service data pulled from several makes and models, the average mileage of replacement for a sunroof motor was after the 150,000 mile mark, which should be an encouraging figure.

If the sunroof will not function, the motor is not automatically considered the point of failure. First, the fuse will be checked and tested for power. Next, the relay and terminals will be inspected for corrosion, and then tested for operation (relay) and continuity. Finally, if the sunroof circuit is receiving power when demanded by the switch, the sunroof motor will be bench tested, since it is suspected of failure. If no power is present at any of these locations, the body control module, or even the switch, the sunroof motor will not be immediately suspected, instead, the sunroof position sensor may be suspected, or the circuit could have physical or electrical damage.

The worst part of replacing a power sunroof motor is that the motor is buried underneath the headliner. This means at a minimum, the headliner will need to be lowered from the ceiling, if not removed altogether. In order to remove the headliner in most vehicles, the interior trim for all pillars must be removed, followed by all overhead mounted assemblies and lights. Then the headliner may have a few fasteners which need to be removed to lower the assembly. After this is accomplished, if it must be removed, a seat or windshield may need to be removed in order to extract the headliner. At this point, the sunroof assembly can be extracted by removing a few fasteners and electrical connections, or the motor may be removed from the assembly if possible. Replacement is the reverse of removal, and noting that special care must be taken to avoid creasing or cracking the headliner, as well as frequent hand cleaning to avoid staining the headliner with the thick abrasive grease used in the sunroof regulator assembly.

Whenever there is a failure in the sunroof, especially if it is left open, we recommend immediately consulting the owner's manual for advice on how to operate the sunroof without battery power or a properly functioning motor. This can save time, frustration, repair costs, and undue damage to the vehicle's interior.

If the sunroof is open while the vehicle is having issues with the battery or other charging system components, it is highly important that the sunroof be closed immediately. This will prevent the issues mentioned above from coming to fruition. If a vehicle with a bad sunroof motor must be left outside, the roof area should be covered with a tarp, or the sunroof should be sealed with a non-permeable membrane and a clear coat-safe tape. Even if some water penetrates under the tape, it will likely drain through the sunroof body drains instead of entering the interior of the vehicle.

Replacing the sunroof motor or assembly can be an extremely tedious job. However, if the headliner does not need removal, the sunroof motor is known to be faulty, and the tools are on hand, most people with some DIY experience will find this a long but simple job. If diagnostics must be completed on a modern vehicle, a solid understanding of computerized electronic circuit testing is needed.