Driver's Seat Power

[andyman32]

Hi,

I just bought an E34 ('94 540i) two weeks ago. The power to the driver's seat motors keeps cutting out. The dealership fixed it, then it went out while I test-drove it. They fixed it again, and it went out on my way home from picking up the car!

The heater elements work on the seat, even when the motors are not.

Anyone else had this problem? Is there anything I can do to the wiring under the seat myself? There's a circuit board with 4 black fuses (might be fusible links) under there. Any ideas?

Thanks!

[Javier]

there is Fuse 42 and Fuse 43 (30A each) for passengers and drivers seat respectively (located under the rear seat), hard to believe both fuses went together. If both seats stop working together and everything else is working fine (stereo system for example, Fuse 36), then the problem is very rare, as grounding pads are different also for both seats. The only thing I can imagine, without having the chance to put my hands on, is that fuses were blown and are being replaced with very small ones, keeping them blowing one after the other.

[andyman32]

Thanks ofr the reply. It's not both seats; the passenger's seat works fine. It's just the driver's seat. It appears that the dealership fixed it *TWICE* by just replacing the fuse, but it went out again during the next drive. I've got the Bentley's manual on the way... hopefully that will shed some light on this!

[Javier]

If the replacement fuse was 30A, and blows again, then consider this procedure.

Unplug the under the seat connector and put in a new fuse. If fuse holds, then the fault is located under the seat, otherwise, check the harness from the rear distribution box (under drivers side rear seat) to the drivers seat looking for signs of insulation wear out.

Verify that the electrical harness under the seat is not wear out nearby the metal edges it runs close to, plug the connector and check the fuse, if the fuse holds, then the problem is after the switches.

Operate the motors one by one, in order to identify which one is causing the fuse to blow. Verify the power seat is running smooth, free of obstacles, if you feel any motor overloads, this may blow the fuse over time, the corresponding mechanism should be cleaned and lubricated.

Once identified the motor circuit that blow the fuse, check carefully the lines feeding that motor from the switch. If nothing seems wrong, the motor may be in trouble. Remove the electrical connector to that motor, put a new fuse and operate the switch (This will verify the switch is not short circuited inside).

Feed the motor straight from the battery, you can wire trough a 40A fuse and check if motor operates freely, you may also remove the mechanical load of the motor, if fuse blows no mater its loaded or not, then you will need a new motor. If it blows only under load, verify there are no mechanical obstacles to the motor operation, clean and lubricate, if every thing is OK but the motor keeps blowing the fuse, the you will probably need a new motor.

Here is a link to you car circuit schematics. The Power seats link and the Fuse details link (for fuse 42), are the drawings you will need to debug.

http://www.carsoft.ru/avtorepair/bmw_e34/E34.html (http://www.carsoft.ru/avtorepair/bmw_e34/E34.html)

This drawings does not apply to memory seats, nor I can offer you drawings for those, but debugging criteria should be similar.

[andyman32]

Thanks for the tips Javier. It appears that the fuse only blows when the motors are under high stress - that is, the fuse doesn't blow moving around the seat, but it blows as soon as I sit in the seat and try to move any of the motors.

You think this means I need new seat motors?

[Javier]

Hard to believe, unless you focus the problem to one motor, I would rather think on lubrication, even inside the in tube driving wires from the motor to the seat mechanism.

[winfred]

id be thinking almost shorted wire, when you the squash the seat it grounds out

[Javier]

nt

[andyman32]

Yes, good thinking, thanks... I will have to check the wiring harness. You might be right. The passenger's seat does not have this problem.

Additionally, the driver's seat HEATER still works even when the motors blow the fuse. However, that's neither here nor there, since it's on a different circuit.

Thanks for the help guys... I'll keep ya' posted on what I find! :)


id be thinking almost shorted wire, when you the squash the seat it grounds out