Brake Wear false alarm?

Hi folks, On my current 996, I am getting a brade pad wear alarm, but when I visual inspect the pads, it looks like I have plenty of pad left. Anyone ever seen a false alarm on the break wear warning? Maybe I am not looking at the right place to determine the amount of pad that is left? Thanks, Greg

Hard to tell without seeing the condition of the sensor. Is the break wear sensor on all the time or does it come on periodically and then go away? You could easily have what I did on my SUV pads. The pad cracked near the sensor and the sensor circuit was cut premature. Another explanation is if the light comes on IMMEDIATELY after washing your car and then goes away. THat is normal. Yet another explanation is........... well you see where that is going

The Sensor comes on after driving the car for 5 to 15 minutes and then does not go away. I have about 3/4 cm left on my pads. Thanks in advance!

My guess is that your pads are about ready to be changed. If you are at about 7mm (3/4cm) then it is VERY possible you have tripped the sensor. With that much pad left and if you are planning on doing another track event I would change the pads now. Last thing you want is your pads to leave you while on the track!

Your brake fluid may be worn/boiling as well. That happenend to me at Limerock, the wires were melted into the pads.

A good rule of thumb is to compare the thickness of the brake pad material to the thickness of the steel pad backing. The pad material should be at least as thick as the backing. I don't visualize metric lengths very well, but Dell is right that you may have worn into the sensor wire, in which case it is not a false alarm but it is operating properly. I once had a problem similar to yours, and it occurred because I had actually melted the plastic area around the sensor (at Mid-Ohio ) I have to admit it was a little disconcerting to see the light come on at the end of the back straight. When this happened, I had plenty of pad left and the sensor was actually intact. After that point, it would sometimes illuminate if there was too much moisture. Then, I did what all the people do who self-inspect their brakes regularly: I pulled out the sensors and zip-tied them out of the way. If I ever want to reinstall them, I just have to clip the zip tie and stick the sensors back in the brake pads.

If your wires are melting, then your fluid is boiling. Good idea to flush it several times during the season.

New pads are 10 mm thick. If yours are 7mm then you have plenty of pad left. The sensor may be cracked. Heat makes the plastic carrier expand and open the crack enough to break the circuit which sets the alarm light.

FYI - The pad backing material is approx 5 mm. Sensor is 'supposed' to light at 2 mm, so you want to change at 2.5 mm to reuse the sensor. If tracking you'd want to change if below 5 mm.

The brake pad wear sensors are simply a continuity loop wire that is stuck into the brake pad. The dash light is triggered by an open condition on any of the pads that the wire is looped through. As the pad wears away, the wire loop will come in contact with the rotor and will be cut, breaking the continuity loop and setting the light on. A false alarm situation can occur if there is a high resistance situation in any of the sense wires that go to the pads. This can be because of a nicked or cut wire, or a corroded or loose cable connector. The sensor logic will interpret the high resistance as an open connection and thus set the light. Sounds to me like you have a nicked sensor wire, or a corroded connector. The main connectors for each brake's sensor wire is back behind the brake caliper. I would check those connectors for being secure and clean, and then look at the thin wires that go into the pads for cuts or breaks. I'm not sure where you live, but if the car has been driven in wet slushy conditions lately, and the connector is loose, then the connector is probably corroded, and needs to be cleaned and reset securely.

Thanks for all this! Could it be just overheating? I just drove the car around for a while and the brake wear light never even came on? I am in Socal - so i doubt it is rust..

If it is intermittent like you describe, then it is probably either a cut sensor wire, or the electrical connector on a caliper that has corrosion on it or is not seated properly. This is causing borderline high resistance on the sensor line and tricking the monitor logic into thinking that there is an open circuit, hence the light comes on only sometimes, or goes off after the car warms up, etc. I doubt seriously that this issue has anything to do with overheating calipers. The insulation on the sensor wires has a much higher melting point then the calipers can achieve, short of the pads catching on fire. And in that case the light coming on is the least of your worries. I would check the sensor wires on each caliper for damage, and reseat the connectors. Good thing is that the sensor wires are designed to be replaced and are about $20.

FWIW, the brake wear warning light also came on recently in my C4, it is intermitten. It is always off when the engine is on/off cycled, and then would come on sometime after 10-15 minutes of driving. It did get better after I washed the car ans sprayed a lot of water int he brake caliper area, which took longer to come on... Stupid thing... Anyways, but I think the rear pads are worn out... So..... Since we are talking about brake pads, do you guys use the factory dome shaped anti squealing shims plate back on the new pad?