My warning lights keep coming on for my brake pads. Took it to my dealer who checked it over confirming that all the pads are fine. Still happening tho. Any solution, any one?
I don't think your idea will work. The brake service message works by detecting a discontinuity (an interruption in the circuit) of the single wire leading to and then from the brake pad.
If you disconnect any one of the connectors, you will see a continuous brake service message.
A much easier way would be to run a diagnostic scan and see if the vehicle reports which of the four wheels is sending the message (I'm not sure if it gets that granular, but it can't hurt to try).
An alternative method would be to create a jumper plug that MAKES the circuit across the connection where it plugs into the brake pad, and then try using this jumper plug on each of the four wheels - checking individually to see when the warning message disappears.
About 10kmiles ago I had the same experience: brake pad light stubbornly on, but visual inspection indicating there was still enough material for maybe another 7-10kmiles. I changed the pads anyway, since at almost 50kmiles I felt I had gotten excellent service from them, and the light wnet off immediately and has been off ever since. I think the moral of the story is that the sensors are designed to give ample warning long before the pads are completely worn out.
The way brake service messages work is by embedding a small wire in the brake pad, so that when the brake pad is too thin, a contact is made between the wire (that now protrudes from the pad) and ground (the brake disk).
So the car is expecting a contact to take place, and not an absence of contact (or, as you say, a discontinuity in the circuit).
Having an interruption in the circuit means the pad is healthy, as it prevents the contact from taking place.
So, disconnecting the wire would make the car think that the pad is good.
Disconnecting all wires should remove all warning, unless, there is a short between the wire leading to the brake sensor and some part of the car.
Either the short takes place between the brake sensor connector and the car computer (in which case it can happen anywhere in the wire mesh) or (more probably) the problem lies in the sensor.
Reconnecting each wire one by one should tell you which wire is faulty (connecting the faulty wire will light the brake warning).
Unless I have grossly misunderstood the principle, there is continuity in a new brake pad, and when the brake pad eventually wears down, it wears through the wire and breaks the continuity - rather than establishing continuity.
I suspect that we are probably both in agreement about the general concept, but are using different terms to describe it.
Brake Pads - New and Worn (indicator wiring at top)
I think if you look carefully you could believe that there are actually two wires in a common sheath. In the self study guide (posted in a thread regarding long life servicing recently) there is a circuit diagram that shows the two wires.
self study guide here: http://www.volkspage.net/technik/ssp/ssp/SSP_224.pdf
Last edited by n968412L; 04-17-2011 at 03:51 PM.
Yup, the old Mercs do work like that (or at least the W140 I have some experience with does...) but if you look at a worn sensor pad from the Phaeton, you'll see two little copper points where the wire has worn away. I think the logic is that once the sensor is worn, the warning is displayed constantly rather than just when you press the brake pedal.Originally Posted by Zaphh
Perhaps check that the wires are in place. I actually had a sensor wire brake which caused the sensor to go off. Unfortunately, some of those wires are built into the pad which caused me to replace the entire pad. Another possibility (although remote) is that the wire came unplugged.
No. Try not. Do... or do not. There is no try.
the "check brake pad" light appeared in dash panel. As all we know diagnostics doesn't show which of brake pads,front or rear, it's time to replace. So my questions - is it possible somehow to know which of brake pads (front or rear) should I change? Or should I change all four brake pads at once?
Thanks for any of your opinion.
Depending on the thickness of your rotors, that might not be the most cost-effective plan. I'm just about to change my front pads, the rotors are a shade over halfway through their life, and the pads are about 70% worn. If I wait until the pads are done, the rotors will need replacing too.
I think so. A set of pads is $140 after haggling, but rotors are about $250 for the pair, then there's the extra labour or time if you DIY. It'd be even better if they'd switch to the caliper design that my 951 has, there's a spring clip arrangement on top of the pads, so it's just a case of flipping that up with a pair of pliers, pushing back the piston, then swapping the pads. Takes about 10 minutes a side.