PaulW

We've had some discussion on this lately, and Heinz Wimer had emailed me asking about how to troubleshoot it.

The brake pad warning light circuit is a ground path loop. When this ground path is interupted (open circuited, like turning a light switch off), the brake pad warning light (K32 in image) comes on.


<img src="http://www.audipages.com/Tech_Articles/susp_whls_brake_steer/brakesensor1.JPG">

The path it takes is from the back of the instrument cluster (pin 25 on red 26 pin connector), through the firewall somewhere, to T3g, pin 1 (3 pin connector back left of engine compartment) to N13, which is the brake pad wear indicator, left. It then goes back to T3g, pin 2 and over to T3h, pin 2 to N12, the right brake pad wear indicator. Then back through T3h, pin 1 which is then connected to chasis ground at point 83. 83 is ground connection 1, in right front wiring harness.

Follow that path, it goes from the sensing circuit which is at 12 VDC to ground at point 83 which is chasis ground. When this circuit is interupted, the light comes on. Easy? Yes, it really is.

So how to troubleshoot? Pretty easy. Find three pin connectors T3g and T3h in the engine compartment.

Take a continuity check from the brake pad side of pin 1 on T3g to the brake pad side of T3h pin 1. You disconnect these connectors, hook up a multimeter on the resistance range, and you should have 1 ohm or less for continuity.

But if your brake pad wear light is on, it will probably be an open circuit (greater than 2000 ohms, most likely infinity).

Measure the continuity across each of the brake pad wear indicators as shown in the image. One will most likely be shorted (continuity) and the other will be open circuited. Find the one that is open circuited and repair as required by shorting the brake pad wear sensor wires. You probably put on aftermarket pads that didn't have them and now the old ones need to be cut and twisted together to create the ground path.

If these circuits tested good, then take a resistance reading from the ground side of T3h pin 1 to a known ground location. You should have continuity (short circuit). If not, troubleshoot and repair wiring.

If that tests good, pull the instrument cluster and check continuity from T26 pin 25 to T3g pin 1. There should be continuity. If not, repair wiring.

Want to skip all these tests at first? Find T3g pin 1, and connect the instrument cluster side to ground with a jumper wire. Turn the car on, did the brake pad warning light go off? If so, you know the problem is down stream. You could reconnect it and do the same from T3h pin 2. If the light is still off, you know the problem is down stream of that point.

I will make a page on audipages for this. BTW, this is for 97-99 wiring, couldn't find the 00 and newer wiring on the Bently, but I probably could if needed to.

pw

nanohead

I use EBC greens and sure enough, they are flaky with the warning light.

I think I'll go back to stock pads anyway, as these pads are not a real improvement over the stock pads (other than price!)

I was actually surprised to discover that there is no information about brake pad condition or the state of the brake pad warning light in the brake controller or any other place within the diagnostic infrastructure of the electronics.