A- One Seat Repair
Surprisingly, seats present some of the most complicated components on any car. When you start adding bells and whistles to them (like heaters, occupancy sensors, power motors, and air bag sensors), you end up with a complicated device that gets a lot of use and often needs some attention. This project covers three basic repair procedures involving the E36 power seats: seatbelt receptacle replacement, seat occupancy sensor replacement, and power seat switch replacement.
The first step is to remove the front seat, which is a pretty easy task. Unbolt the seat from the chassis floor according to Photo 1. Then disconnect any electrical connections that may be located underneath the seat (Photo 2). Because each seat weighs between 60 and 80 pounds, I suggest that you have a helper assist you in lifting and carrying the seat from your car. You’d hate to lose your balance while lifting and bang your seat against the side of your car.
With the seat removed, you will have relatively easy access to the remainder of the seat components. The belt buckle receptacle can easily be replaced once the seat is removed from the car (see Photo 1). The electrical switch inside this receptacle often fails, resulting in air bag warning lamp error messages (see Project 83). Replacement is as simple as unbolting the old unit, attaching the new unit, and running the wire harness through the seat.
The passenger seat occupancy sensor is used to tell the air bag computer whether or not there is a person sitting in the passenger seat. This avoids a potentially costly deployment of the passenger-side air bag if there isn’t anyone sitting there. This sensor gets lots of use and is responsible for a significant portion of air bag lamp faults. Once you have determined that this sensor is the cause of the problem, replacement is fairly straightforward and costs about $85.
To access the sensor, you need to remove the lower seat pad. This pad is attached at four points, sometimes with screws and sometimes with plastic clips (see Photo 2 for removal instructions). With the pad removed, the sensor becomes visible. It is simply tacked down to the lower seat cup by double-sided tape that comes pre-attached to the sensor. To replace the sensor, simply pull off the old one and stick on the new one. Reroute the wire harness for the sensor underneath the seat. Before buttoning up the seat completely, I would carefully carry it over to your car and plug it into the wire harness to see if the air bag computer still gives an error message (for this, you will need an air bag reset/code reading tool like the one described in Project 83). It’s better to find out now if there is a problem with the assembly than after you have reinstalled the seat.
A note of caution: Do not put the key into the ignition with the seat removed if you are not having trouble with your air bag. If you put the key into the ignition and turn it on with the seat disconnected, the air bag computer will register a fault, and the light will go on. Then you will not be able to reset the light without a code reset tool.