Brake wear indicator light... brake pads not worn out ?!

[redriver666]

Last week, the brake wear indicator light came on on the dashboard Since you can't tell which brake pads are involved on a Boxster 986 (and it can't be diagnosed via Durametric either), I removed all the wheels today and visually inspected the pads. Just as I expected (I don't drive many miles a year), none of the pads were worn down to the wear indicator; in fact, all the pads still have at least 3 to 4 mm of material left before reaching the indicator To be safe, I also disconnected the plug at each brake pad to measure the resistance; a short circuit in one of the plugs could potentially trigger a false warning. Below are 3 photos of the "operation".

Questions:

1. The resistance value shown on the multimeter (for all 4 brakes) is identical to that of a new wear indicator (which I had already ordered). Does this mean there is nothing wrong with my wear indicators?
2. What, then, could be the cause?
3. Is it true that the dashboard light only comes on when there is a "closed circuit"? In other words, when the wear indicator makes contact with ground/the brake disc?

But now for question 4:

4. After reinstalling all the old pads and indicators... the dashboard warning has disappeared (for now)... :? Anyone have an explanation?

[tcoradeschi]

Originally Posted by redriver666

Last week, the brake wear indicator light came on on the dashboard Since you can't tell which brake pads are involved on a Boxster 986 (and it can't be diagnosed via Durametric either), I removed all the wheels today and visually inspected the pads. Just as I expected (I don't drive many miles a year), none of the pads were worn down to the wear indicator; in fact, all the pads still have at least 3 to 4 mm of material left before reaching the indicator To be safe, I also disconnected the plug at each brake pad to measure the resistance; a short circuit in one of the plugs could potentially trigger a false warning. Below are 3 photos of the "operation".

Questions:

1. The resistance value shown on the multimeter (for all 4 brakes) is identical to that of a new wear indicator (which I had already ordered). Does this mean there is nothing wrong with my wear indicators?
2. What, then, could be the cause?
3. Is it true that the dashboard light only comes on when there is a "closed circuit"? In other words, when the wear indicator makes contact with ground/the brake disc?

But now for question 4:

4. After reinstalling all the old pads and indicators... the dashboard warning has disappeared (for now)... :? Anyone have an explanation?

I’ll do my best.

The wear sensors are actually loops of wire, and so are close to being a short circuit (the 0.3 ohm reading that you see may well be intentional, to limit current thru that circuit). When the pad wears to the sensor, the rotor will cut it, and the resistance will increase. I believe that all four corners are wired in series, so all that the system can tell you is that one of the eight pads has worn to that point. What level of increased resistance is required to trigger that warning? No idea.

As to why your dash light came on, I would hypothesize that one (or more) of the connectors where the sensor plugs into the wiring harness was either loose or slightly corroded - most likely the latter. By disconnecting and reconnecting all of them, you cleaned up the connection, and the false positive has cleared itself.

Regards,
TC

[BrakeExpert]

I agree this is possible. Yes these aren't actually sensors, its a very basic wire that gets severed. The fun part is when it gets cut and rubs against the rotor so the car still doesn't think they are worn.
Other answer is that age old crummy German wiring. We don't get those good ol Japanese rubbers and plastics :P

[redriver666]

I removed and reinstalled the front components (pads + wear sensor), but the error persisted, so the front doesn't seem to be the cause. I then did the same for the rear, and the error message disappeared. So, the issue was at the rear. It was a mistake on my part not to check the dashboard warning after doing the left side; that way, I would have known whether it was the left or right side. Oh well, I'll see how it goes from here. A possible internal short in one of the sensor cables or corrosion creating a closed circuit, triggering the warning is indeed possible. Aging cables could be a factor. In any case, I already have four new sensor cables ready to install if the warning returns and the pads aren't actually worn out.

[Burg Boxster]

most likely issue is brittle wire casing... One vehicle in my stable is 15yrs old and though I've replaced pads/rotors multiple times, I've always been able to reuse sensors. Kind of a sport - LOL.

Anyhow, one sensor finally gave up the ghost and instead of plopping down the $5 per corner, I simply shorted out the loops and heat shrank remaining tail. Light off and all is good w the world again.

You seem well versed mechanically and truly all you need to do is twist the bare conductors together, seal up, and done. Caveat emptor but keep an eye on pad wear as you already do. Bring back the good old brake pad wear indicator noise makers (IYKYK ).

[Newsguy]

As our cars are aging, I now make a point of spraying every connector I come across with some cleaner and put some dielectric grease on it.
I also light a votive candle!
Gotta cover your bases,