Brake lining wear light is on

mnichols · 03-11-2009, 02:37 PM

I have a track car (1995 M3) that I do most of the work on. When I recently started the car the brake lining wear light came on, funny thing to happen since I don't have the wear connectors installed on either the left front or right rear. I double checked the connector boxes where the sensors connect to the car and both looked ok.

If this light is set, does it require a code reset to kill the light, or does removing the sensor problem turn the light off?

I have an OBDI code reader, but its not showing any faults.

Simple failure, or something I should be worried about?

Jeron · Jeron's Garage

If the wear sensors are not installed the light will be on.

The light reset, only requires that you turn the car on but you dont start the car for one minute.

Have you checked that the sensors have not become dislodgeed from where you stashed them?

mnichols · 03-15-2009, 04:04 AM

Jeron,

I've removed the sensors from the car, so the connections are open. There are two wires that go to the sensor. I've measured across the sensor connector on my workbench, and its virtually a short on both the front and the rear sensors. I can't find the information in my books, but does the control unit send a current through the sensor to check for its presence, then if it sees the sensor touch chassis ground light the wear indicator?

Can you create a jumper that goes across the connector on the car to make it believe a sensor is present?

mnichols · 03-15-2009, 07:02 AM

Are there any technical manuals out there, either factory manuals or aftermarket that give a theory of operation on the the control unit and its sensors?

Manolito · 03-15-2009, 08:04 AM

According to Bentley's, on your car, current runs from pin 7 on the instrument cluster through the front sensor, then the rear sensor, then to ground.

Whoever removed the sensors must have grounded the wire that went to the front sensor, or the light would have lit immediately. Apparently, that ground has come loose.

mnichols · 03-15-2009, 09:43 AM

Manolito, Interesting. I also have a copy of the Bentley Service Manual for the E36 3 series, but couldn't find the information you quoted. Maybe I don't know how to search through the manual, or perhaps I have a different book?

Which book do you have, or help me understand how to find it in mine.

mnichols · 03-15-2009, 01:34 PM

I found the instrument panel wiring diagram as you described in the Bentley manual. I pulled the left front wheel, and opened the connector box for the sensor. I used the old sensor plug and cut the wires coming out of the plug, reinstalled the connector in the panel and traced which one went to the rear connector and which one went to the instrument panel. I grounded the wire that went to the panel, and packaged the modified connector back into the panel. Works perfect!!

Thanks again for the advice, I've found much more value in the Bentley manual now that I'm paying attention to the wiring diagrams.