BMW 840i Power Seat Control Module Replacement Cost

Power seats in a car, truck, or SUV allow for the driver or passenger to custom tailor the shape or position of the seats for maximum comfort at the push of a button. The power seats are adjusted with a number of small motors inside the seat. The operator presses a control switch that signals the power seat control module to trigger a relay that turns on the motor. 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). Some vehicles with a heated seat option may locate the heater switch with the power seat switches as well. With some vehicles, the control module is an electronic control unit (often mounted under the seat) that is separate from the switch assembly. With other vehicles, the control module is integrated into the switch assembly.

The seat control module receives electrical current from one or more switches that, when actuated, send signals to relays that control the power seat motors. Adjustments are coordinated - in some cases 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.

Symptoms of a malfunctioning power seat control module might include the seat not moving in one or more directions when the switches are actuated, or the seat not moving at all. On vehicles equipped with seat heaters with controls mounted with the power seat controls, inoperative seat heaters may be a symptom of a faulty control module. Also, in some cases, seat setting memory loss may result from a bad seat control module. Occasionally, a dead battery or a blown fuse can be a symptom of a bad control module as well.

If the cause of a faulty power seat control module is a short circuit - or the problem leads to a dead battery (requiring reset and relearning of vehicle systems) - immediate attention should be given to the problem. The vehicle should be driven as little as possible. If a bad control module leads to the power seats not functioning, the seats may not be able to adjust properly, leaving the driver in a compromised position while driving. The condition should be resolved as soon as is reasonable. 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 control module switches may wear out over time. Damage can occur to wiring or a control module mounted under the seat, especially if water is allowed to pool on the floor, such as may occur in a flood.

To check for a bad power seat control module, 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. The technician will also check to make sure that power is present at the control module by performing a voltage test with a multimeter. A bad control module - or a problem with the Body Control Module - may also present a diagnostic trouble code (a fault code) that can be read with a scan tool.

To replace a power seat control module located under the seat, the technician will remove the fasteners that hold the seat to the floor. This may be a difficult job if the seat is unable to move to reveal the fasteners. The seat is gently tipped forward for access to the wiring and to the power seat control module. Care must be exercised in order to prevent strain on the wires that could cause damage. The control module is located, the electrical plugs disconnected, and the retainers removed. With the bad control module out of the way, the new one is installed in place and connected. The seat is returned to its mounts and the fasteners reinstalled. On some vehicles, reprogramming of the power seat control module is necessary. If the control module is part of the switch assembly, removal of the seat may not be necessary.

RepairPal recommends that a power seat control module be replaced with an OEM part that will integrate properly with the vehicle electronics.

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.

As with many repairs on a car, truck, or SUV, difficulty lies more with proper diagnosis of the problem than with the replacement procedure. Such is the case with the power seat control module. While it may be difficult to move the seat for access with the power seat unable to adjust, and while there are sensitive wires that need to be protected, still it is more challenging to determine whether the control module is actually at fault. Anyone with intermediate DIY experience should be able to replace the module, but a professional technician will have access to the tools, diagnostic equipment, and data necessary to comprehensively test the system so that only the relative part is replaced.