Brake pad warning light question

[beemerbird]

Shortly after christmas, I had to really slam my brakes on to avoid some character driving on my side of the road. This brought the brake pad warning lights on.

Since then, the light sometimes comes on when I encounter pot holes, sometimes when I brake regardless of speed travelling, sometimes when I'm not braking and sometimes not at all regardless of braking speed and style.

I've had a look and the pads look to have plenty of meat on them, so I was hoping that someone could explain the workings of the brake pad sensor so that I can get to the bottom of the problem - I'm assuming it's some kind of proximity sensor that kicks in when too close to the discs?

Any advice gratefully appreciated.

Fi

[simonsimoff]

It's nothing more than a couple of wires that run into a small piece of plastic clipped into the brake pad.

When the pad gets low enough on material the plastic of the sensor wears through and the electrical connection between the two wires breaks and the check light comes on.

As a result they need replacing once they've triggered the light to come on like that but a lot of people just bodge it back together with a small loop of wire in place of the sensor to make to check light stay off.

It should be pretty easy to check the state of the sensors on the car - there's one on one of the front brakes, and one at the rear.

[beemerbird]

Is it possible therefore that potholes and sudden braking (when the problem first raised its ugly head) could have dislodged the sensor in some way?

If this is the case, do I need to remove and re - fit the pads to 'seat' the sensors correctly?

[simonsimoff]

The sensor itself should stay clipped in securely enough because it's right in the middle of the brake pad and so should be unlikely to come out, but it could be possible for the plug for it to be loose.

You can get at that easily as it's clipped to the back of the brake disc protection plate. It's a two pin plug inside a rubber jacket that keeps water out.

If that's unplugged then the brake warning light will come on and if it's plugged in and making an OK connection, and nothing else in the circuit is lose, then then light should go out.

[beemerbird]

Thanks for your words of wisdom

[simonsimoff]

I hope it helps

[Brianmoooore]

The sensor is simply a single piece of wire embedded in an insulating block. It is connected in a bridge arrangement in the cluster, so that the light comes on when the resistance of the wire increases (i.e. worn through), or it is shorted to earth.
The sensors tend to stay attached unless they weren't fitted properly in the first place, or an old sensor (that hadn't worn through) has been re used, that had been damaged when it was removed from the old pad.
Lights frequently come on just after work has been done on a hub, when the wires from the sensor aren't dressed properly, and wear through on the inside of the well of the wheel rim.
The problem could also be that the pothole finished off the solder joints to the 220 ohm resistor in the instrument cluster. Every cluster I have ever inspected, without exception, has either had these joints in very poor condition or already resoldered.

[beemerbird]

The problem could also be that the pothole finished off the solder joints to the 220 ohm resistor in the instrument cluster. Every cluster I have ever inspected, without exception, has either had these joints in very poor condition or already resoldered.

You're completely speaking my language here, Brian. I shall check this out, too