Brake sensor warning light
07-10-2010, 02:45 PM
#1
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Brake sensor warning light
i'm getting an intermittent brake sensor warning light on the dash, and i know i need to do some brake work as they do squeak more than they should, but i can't really tell if the noise is coming from the front or rear. i'm guessing the front, but it would be great to know for sure before i start pulling things apart. i have a vag-com, and my question is can i somehow use vag-com to tell me which brake sensor is triggering the warning light? i'm just trying to save some time and it would be great to know if it's the fronts or rears that are triggering the warning light. do i need to scan the car when the warning light is on? money is a little tight right now, otherwise i'd just do new pads and rotors all around...THANKS!
Last edited by $chlitz; 07-10-2010 at 02:56 PM.
07-11-2010, 01:53 AM
#2
AudiWorld Super User
I would bet noise is coming from the front. There is no sensor on the rear pads.
No..don't need vag-com. The front sensor is really just a pair of wires that are broken when the pad is worn too far. If you continue to run several thousand miles past the sensor warning and since the disc wears a couple mm inside the outside diameter the metal of the rotor will contact the brake pad backing plate while you still have some pad material left...the pad backing plate will score but chances are you won't damage the rotor.
According to the BB school of brake repair you just cut the sensor wire a couple inches from the connector towards the caliper, strip the wires and twist/solder them together and wrap with tape. Voila..sensor never goes off and you listen for the screech of metal on metal before you replace pads. Or inspect your pads every 5-10K when you change from summer to winter wheels/tires and vice versa.
That being said, the rears COULD be worn...you just have to look at the pads through the wheels. Traction control or electronic stability programs being what they are, spirited driving tends to wear the rear pads. My 2K4.2A6 goes through rear pads as fast or faster than the fronts. The rear pistons could also be frozen or sticking...when they're applied they work but don't retract very well and so they wear a lot faster. You may have to rebuild the rear calipers (don't forget to use some brake-compatible grease on the piston) and don't forget to free up the dust boot on those rear caliper pistons BEFORE you try to twist/retract them. If you twist the boot it will tear and then you have to blow out the piston to reseat the new boot.
Contrary to what others have said, I prefer to use a 4" dia. 1/4" thick grinder to knock off that ridge on the outside and inside of the rotors to minimize brake noise with the new pads. I have the front up on jackstands and a couple of wheel lug bolts with washers or a couple of dies as spacers to hold the rotor clamped to the hub (the lug bolts are too long and will lock the hub if you don't stack the washers). Turn the engine on and put it in L or manual first and let the engine turn the rotor and you run the grinder to knock off the ridge.
PS...don't use Hawk HP Plus unless you really like a LOT more dust than stock or have matte black wheels. I accidentally ordered HP Plus rather than HP Street and now have really black rear wheels on my S6. The dust washes off rather easily but still...
No..don't need vag-com. The front sensor is really just a pair of wires that are broken when the pad is worn too far. If you continue to run several thousand miles past the sensor warning and since the disc wears a couple mm inside the outside diameter the metal of the rotor will contact the brake pad backing plate while you still have some pad material left...the pad backing plate will score but chances are you won't damage the rotor.
According to the BB school of brake repair you just cut the sensor wire a couple inches from the connector towards the caliper, strip the wires and twist/solder them together and wrap with tape. Voila..sensor never goes off and you listen for the screech of metal on metal before you replace pads. Or inspect your pads every 5-10K when you change from summer to winter wheels/tires and vice versa.
That being said, the rears COULD be worn...you just have to look at the pads through the wheels. Traction control or electronic stability programs being what they are, spirited driving tends to wear the rear pads. My 2K4.2A6 goes through rear pads as fast or faster than the fronts. The rear pistons could also be frozen or sticking...when they're applied they work but don't retract very well and so they wear a lot faster. You may have to rebuild the rear calipers (don't forget to use some brake-compatible grease on the piston) and don't forget to free up the dust boot on those rear caliper pistons BEFORE you try to twist/retract them. If you twist the boot it will tear and then you have to blow out the piston to reseat the new boot.
Contrary to what others have said, I prefer to use a 4" dia. 1/4" thick grinder to knock off that ridge on the outside and inside of the rotors to minimize brake noise with the new pads. I have the front up on jackstands and a couple of wheel lug bolts with washers or a couple of dies as spacers to hold the rotor clamped to the hub (the lug bolts are too long and will lock the hub if you don't stack the washers). Turn the engine on and put it in L or manual first and let the engine turn the rotor and you run the grinder to knock off the ridge.
PS...don't use Hawk HP Plus unless you really like a LOT more dust than stock or have matte black wheels. I accidentally ordered HP Plus rather than HP Street and now have really black rear wheels on my S6. The dust washes off rather easily but still...
07-11-2010, 10:40 AM
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wow! thanks for all the info! so what i get out of all this is that there are no brake sensors on the back pads, so if i'm getting a pad wear warning it must be the fronts. i do have slightly more brake dust than usual on my front wheels (which means there is A LOT), so i kind of figured it was probably the fronts. if the brake sensor works as you described, why do you suppose the warning light only comes on intermittently (probably every few days, then goes away for a few days)? i really would rather not bypass the sensors...i like the fact that there is something to tell me i'm going to need brakes soon other than just my ears and sense of feel.
thanks for all the tips...i bought the car 10k miles ago and have not done any brake work yet, so i guess i'll just plan on a complete front brake job (pads and rotors) and then i'll inspect the rears.
thanks for all the tips...i bought the car 10k miles ago and have not done any brake work yet, so i guess i'll just plan on a complete front brake job (pads and rotors) and then i'll inspect the rears.
07-11-2010, 04:16 PM
#4
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OK, you got the gist of the discussion.
But hang in there...the light will go on solidly in a few days. One possible answer is that the pads aren't retracting all the way and the sensor wire(s) are shorting through the pad dust or the rotor, thus turning off the light.
But hang in there...the light will go on solidly in a few days. One possible answer is that the pads aren't retracting all the way and the sensor wire(s) are shorting through the pad dust or the rotor, thus turning off the light.
07-18-2010, 12:07 PM
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did the front pads and rotors today. much easier than expected. still had a brake warning light on the dash after the job was done, but one of the wear sensor connectors on the car was broken, so that probably explains my intermittent warning light on the dash. i probably still had a little life left in the pads and rotors, but oh well...now i should be good for a while. i ended up snipping off the wear sensor connectors and twisting them together, then shrink tube over that and taped 'em out of the way. that took care of the warning light!
thanks for all your help!
thanks for all your help!
07-18-2010, 12:29 PM
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So a closed circuit or an open circuit is what keeps it happy? Did you twist the 2 copper wires together, or just cut it off and leave the circuit permanently open?
07-18-2010, 12:58 PM
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a CLOSED circuit keeps the warning light off. i just clipped off the wires coming from the pad, and then clipped off the connector on the car. there are two wires going to the connector, just strip a bit and twist together. i put some shrink tube on the wire ends and taped the wire back and out of the way so it's not just dangling there.
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07-18-2010, 01:06 PM
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i have no idea. electrics are not my strong suit. i'm sure you could just jumper the contacts in the end of the connector and then just tape it up and leave it in place. or you could leave the connector alone and splice the wires together AFTER the connector (where you snipped the wires off the pad). that way you're not messing with the harness at all, but you still have the potential for a bad connector to set off the warning light.