2003 BMW 540i Power Seat Switch Replacement Cost

The power seats in a car, truck, or SUV can be adjusted to custom positions or shapes for maximum comfort at the push of a button. Power seats may incorporate forward, backward, up, down, tilt, lumbar support, and even headrest adjustments. In many cases, settings for multiple occupants can be memorized by the seat control module (or by the Body Control Module). These functions are adjusted with a number of small motors inside the seat triggered by the power seat switches.

The power seat switches communicate with the power seat control module that coordinates the function of the power seat motors. In some vehicles, the adjustments are memorized by the seat control module. These operations, along with dozens of other functions of the vehicle body (power mirrors, locks, windows, airbags, alarm, et. al.) may also be overseen by the Body Control Module.

A power seat is designed to move in many directions, enabled by several seat motors, each of which tracks along a specific axis (up and down, forward and backward, diagonally). If the power seat is operational but does not move in a specific direction when one of the switches is pressed, a power seat motor may be at fault. More likely, a power seat switch is the culprit. A faulty power seat switch may also cause the seat to work intermittently. If a power seat does not move at all, the problem likely originates from somewhere other than a bad seat switch. Occasionally, a blown fuse can be a symptom of a faulty switch.

If the less-than-likely event that the cause of an inoperative power seat is a short circuit in the switch, immediate attention should be given to the problem. More likely, the problem has to do with worn electrical contacts in the switch that cause it to stop working. While this does not pose an immediate concern, improper seat position (relative to the controls and to the airbags) and improper headrest adjustment are safety concerns for both the driver and the passenger.

Power seat components are intended to last the lifetime of a vehicle and have no regular replacement interval. The power seat switches are the most likely components to wear out and fail over time.

To check for a bad power seat switch, a technician will first make sure that a fuse has not blown. A blown fuse can be either the cause of an inoperative power seat or a symptom. If all of the seat functions stop working at the same time, it is unlikely to be caused by a bad switch. If the seat will not move along one axis when a switch is pressed, but works in all other directions, the technician will use a diagnostic meter to check for power to the switch. If voltage is present at the switch, the technician will test the switch for continuity - whether or not it is capable of transmitting electrical current when operated - and possibly bypass the switch to make sure the seat motors are operational. If the switch has power but will not operate, the switch is likely to be defective. In some cases, the problem might originate in the seat control module or in the Body Control Module. In these cases, the technician will look for a diagnostic trouble code (a fault code) that can be read with a scan tool.

Once a power seat switch is found to be the cause of a seat malfunction, a technician will disconnect power to the seat (or disconnect the battery) and carefully remove any interior trim around the switch assembly. The power seat switches are most often located on the side of the seat body, but may also be found in another location, such as the door trim panel. With the trim removed, the switch assembly is unplugged from the wiring harness, the switch detached from its housing and replaced with the new switch before reassembly. In most cases, all of the power seat switches are contained in a single assembly that needs to be replaced as a unit, rather than individual switches.

Proper seat alignment is important for safe operation of a vehicle. While a faulty power seat switch does not present an immediate danger, it does affect vehicle safety. It is recommended that a faulty switch be replaced as soon as possible.

It should be noted that some vehicles incorporate Supplemental Restraint System (SRS) features into the seat, such as seat-mounted airbags and/or seatbelt pretensioners. Care is needed to avoid damage to the wires for the SRS and other components located in the seats. The SRS may need to be reset with a special scan tool if, for some reason, the seat is disconnected.

In most cases, a power seat switch can be replaced by someone with intermediate do-it-yourself experience. But, as is the case with most automotive electrical problems, diagnosis can be the biggest challenge. A fault in the seat control module or the Body Control Module can make it look like the switch is to blame. Repairs can be costly if not diagnosed properly. Access to vehicle-specific information (such as a wiring diagram) and procedures are recommended for an effective repair.