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I have a Mercedes C class M reg and despite having good brake pads on the front the \'\'brake pad low\'\' light is shining merrily on the dashboard. Anyone had the same problem?
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I would guess that the sensor wire has come off the connector on the pad and it touching some metal somewhere, thereby earthing itself and lighting your warning light.
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If these work the same as the Carlton / Omega ones then the circuit is normally closed; when the brake pad is worn down it breaks the circuit. So any loose connection / snapped sensor wire will cause the warning to activate.
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Audi is the same as SpamCan's.
Works by having a wire running through the brakepad at the wear limit. With additional use of brakepad, wire becomes worn through and circuit is broken, illuminating wear light.
I'm having difficulty imagining how it could work in reverse - by making a connection when worn? Any electronics whizzes have a suggestion?
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Are you sure both pads are OK. Sometimes the inner one is worn down more, but not observed from a 'quick inspection'.
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"I'm having difficulty imagining how it could work in reverse - by making a connection when worn? Any electronics whizzes have a suggestion?"
yes easy peasy, Warning light has power on one side all the time. lamp earth wire goes to brake pad which has metal imbeded at wear point. Pad wears down, shorts on disk, completes earth lamp lights up bingo
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Cheers RF, might me look marginally less daft, even if I am still wrong :D
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My 1986 BMW had brass in the senor which shorted to earth via the disc, once worn through. This was rubbish and would make the light flicker, and only come on when braking at first. My current car is 12 years newer, and works as stated above, a thin wire is broken inside the sensor, once it's broken, that's that, the light or message stays on, and the sensor has to be renewed - at least the old fashioned ones could be reused if you replaced the pads within a couple of weeks, downside was the intermittent warnings, and lack of warning if a wire came off.
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LOL!
Not many of you get your hands dirty on Mercs, do you?
MB use a little brass contact in a plastic holder on the end of a bit of 'curly' wire. The plastic holder clip near the back of the brake pad.
When the brake pad wears the brass contact is bought into contact with the surface of the disc - thus earthing the circuit and putting the light on. The bulb always has a +ve supply and so any connection to earth on the 'downstream' side of the bulb will put the lamp on.
Probably what has happened is that the sensor has come unclipped and is shorting somewhere.
Personally I never fit the wear sensors. I rely on regular servicing and replace pads with less than about 6000 miles of wear on them.
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Probably what has happened is that the sensor has come unclipped and is shorting somewhere.
Hurrah!!!
That means I was right!
Didn't see that coming from half way through this thread :D
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>> Probably what has happened is that the sensor has come unclipped >> and is shorting somewhere.
Or the wire itself is shorting against the frame somewhere. They are usually well-sleeved though - so check the sensor first.
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Two things, firstly when the discs are badly worn and lipped the sensor wire can get cut through whilst there appears to be plenty of pad left, secondly a) does the car have rear discs,b) if so is it the rear pad sensor ??
Andrew
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Simplicate and add lightness!!
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LOL, Aprilia - some of us never go the chance to get our hands dirty on the brakes before it was nicked!
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