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Brake Lining Warning Light Problems.

From: "Laurence G. Hoffman" <>
Subject: Brake Pad Lite
To: "BMW (Digest-Reply)"
Several days ago, I asked for help with a friend's E30 brake pad indicator lite. I want to thank those of you who replied. After checking for open circuit or grounded circuit in the pad sensor wiring, my friend pulled the instument cluster. As I understand it, He jumpered the two electrical pins in the cluster connector where the two wires from the sensors come into the connector. If the problem was in the sensor circuit (and not the circuitry/ board in the cluster) then the lite should have gone out with the jumper installed. It did not. Anyway, my friend checked the circuit board and found a green resistor that was loose (cracked solder). He resoldered the resistor & resoldered some other points that looked questionable. When he reconnected everything, the lite was out. Don't know if he checked the circuit to see if the lite would still come on under the right conditions, but I bet he did.

The following are the two helpful replies to my original post. (Also thanks to, Pat Egan, Harvey Chao, and Benton Adair.

[From: Jim Shank ] This is the topic of the "Calabresions" article in the May 1996 Roundel--page 81. In brief, this is often a problem in the instrument cluster circuit board --like a bad solder joint. If your friend really has verified it's not at the sensors in the wheel, he'll have to remove the inst. cluster to track it down further (even if it's not on the instr. cluster board). See the article for details.

[From: (Paul R. Reitz)]
The following info is for a '91 E30 (325 iX), but is probably the same on all other BMWs. The circuit is as follows: from battery (+12v) there is a series resistor (4.7 kohm?) to a long piece of wire that goes first to one wheel sensor,loops through the sensor (yes, the sensor is just a loop of wire!), runs to the other sensor, loops through that sensor, then terminates at the input of a voltage-sensing circuit at which point there is a (3.3 kohm?) resistor to ground. The electronic circuit lights the warning bulb if the voltage at the end of the loop drops to near zero.

Several things can cause this:

--Paul Reitz