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Discussion Starter · #1 ·
The "Check brake pads" light came on in my 95 325is yesterday on the way home from work. I decided to change the pads front and back because I hadn't done it on this car yet. I got all the new pads on without much difficulty and re-used the pad wear sensors. They didn't look damaged although there were a few cracks in the wire insulation. No bare wires showing though. I took it for a test drive afterward and everything seemed OK. No more warning light. Well, on the way to work today, after about 10 minutes of driving, the red warning light came on again! Now there's definitely nothing wrong with the pads... And yes, I checked the brake fluid level after I finished the job. :) The sensors appear to be some sort of magnetic pickup device that probably detects when the pad reaches a certain distance from the rotor, indicating time to replace. Do they go "bad" as a rule? Do you need to replace them along with the brake pads? Is there some sort of reset you need to do once the warning light goes on? I'm not one for just replacing parts without a reason... Thanks for any insight.
 

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The Canadian Prick.
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THe sensors are designed in such a way as if they tell you that the pads need to be replaced, then the wire has been worn through and the sensor needs replacing now too.
 

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BMWCCA HPDE Instructor
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Yep. Once the light comes on, the sensor must be replaced to turn it off again. If you want to reuse brake pad wear sensors, you have to change the pads before the wear sensor illuminates.
 

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Cruising 280 Top Down
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The sensor is actually pretty simple. It has a small current pass through it and when the current stops (open circuit) the warning light comes on. The fact that your light came on indicates that the sensor is bad. USUALLY that means the brake pad is so worn that it also destroyed the tip of the sensor, opening the circuit.

I just replaced my sensor this past weekend and I could see it wasn't the tip but the wire that had worn through. Go ahead and replace the sensor, it's pretty painless and the part is like $15.
 

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Discussion Starter · #5 · (Edited)
Yes, I did inspect the existing sensors and didn't see anything wrong. The little bubble tips were still there. In fact, the pads weren't worn to the point where the sensor touched anything. I guess the wire could have gone bad or lost connection and that caused the warning light to come on. I only took the sensor off the pad end. I didn't check where the other end connects. Maybe there's a corroded connection there. At least I know the brakes are good, regardless what the sensor says... When time permits I'll look at that. If I need new sensors, so be it...
 

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I doubt the connection would be corroded, they have nice little snap-shut enclosures, more then likely a broken wire somewhere. No big deal, might as well replace them while you are in there.

My braking system was SH!T because of whoever owned the car before me. I installed all new ss lines, new pads, rotors and rear sensor. Now I just bought a new front sensor, and a whole set of 4 calipers to rebuild, paint and install (I have 1 seized caliper right now making the car undrivable), and already have about 50% new fluid in the lines. So by the time I get done with the brake overhaul, the entire system except the pedal and master cylinder will be basically brand new.
 
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