Brake warning light
 

My brake pad warning light on the E300 came on this evening. I've driven the car 210 miles since February, so it sits a lot. Today I took it to fill it up and all was well. This evening I washed the car and drove it twenty feet into the garage and the low brake pad warning light came on. I did give the wheels/rotors a good shot of water, so my first thought was maybe in the morning when everything is dry, things will be okay. Then I looked at my last service I did 5000 miles ago and the front inner pads were at 3 and 4 mm respectively. I really can't think of a reason other than the sensor contacting the rotor for the warning light to go on. Is there?

I've got a thousand mile trip to make next weekend. How much leeway do I have before I damage a rotor(s)? Depending on your answers, I may be doing a brake job in the next few days.

If you were at 3 and 4mm 5000 miles ago, you're probably worn through the sensor bar in the brake pad. Time for a brake job, especially if you're going on a long trip. You're a fool if you don't.

Fool replying here Diseasel. :)

So I did order new brake pads and sensors for the front with the hope of either replacing the pads or taking the new parts with me in case I needed them. However, the new parts didn't arrive until after I had left. So I made the 900 +/- mile trip. Had no low brake pad warning light come on the whole trip and no issue with the brakes.

I just finished washing the car after the trip and lo and behold the second I depressed the brake pedal to put the car in the garage, on comes the low brake pad warning light again. So my initial hope seems to be correct, i.e. there must be either break in the sensor insulation or water is getting to the connection point of one of the sensors, thus causing a short and allowing the light to come on. Make sense?

So there is no doubt that I am getting close to needing new pads, but they don't have to be changed yesterday.

Finally got around to replacing the front brake pads. Here's what they looked like with 99K miles on them. They were between 2 and 3 mm.

A better pic would've been from the side. That way, the pad thickness would be displayed. And everyone could flame you for letting them get that low and taking a 1K mile trip on them....lol. Just messin witcha....

Is it same to say the pads were not worn into the sensors?

If not, there’s probably some other intermittent short in the system.

The point where the harness mounts to the caliper I believe is electrically conductive, remove and clean both sides, harness and caliper. I’d also get dielectric grease on the connections for the sensors and further up the circuit.

You can see from my photo above that the brakes were worn down to the point where they tripped the sensor(s). Funny thing is that not once did the low pad warning light come on during my 1000 mile trip. It only came on after two washings, one before and one after the trip, but then it did finally come on during a little shorter trip around town. I had ordered new pads before my trip, but they didn't arrive in time. All turned out okay though I suppose.