as067

Hi all; I've been lurking on the Board for a few months now and thought it time to get involved. I bought an 85 928S Garnet/Saddle back in August and have been confounded by the brake pad warning light that comes on every time I drive, sometimes sooner, sometimes later. Mechanic checked, said brakes were fine but could not get warning light problem corrected. I read that the brain under the dead pedal can be disconnected/reconnected to reset for major warning lights. Is this a wise/simple solution to my problem? Any precautions I should take? Small concern, but annoying. Any input would be appreciated. Thanks, and I enjoy the board with all the helpful info.

Randy V

Welcome as067 (feel free to use your real first name on your signature line).

Sounds like you have a brake pad sensor fault. The sensor is a small plastic-encapsulated groundfault switch that rests within a notch on one brake pad at each wheel.

When this sensor begins to wear away due to a thin brake pad condition, the rotor removes the plastic covering of the sensor then completes contact of the two metal points within the sensor, resulting in the warning light.

Your intermittent warning light is probably due to either a sensor that had been compromised and not replaced, or a loose wire/connection in the sensor wiring harness. Inspect each sensor for integrity, ensuring that each sensor wire is firmly plugged in to the wiring harness connector behind each wheel. Replace any worn sensor(s) - about $20 apiece.

An interim fix on a worn sensor is to clean it well, then apply a thin coat of 2-part epoxy glue over the exposed sensor face to stop the intermittent warning light caused by water or brake dust shorting across the exposed contacts.

as067

Thanks for the input. Failed to mention in original post, the warning light comes on when turning the wheel sharply or hitting bumps in the road. Would this change the remedy? Thanks again.

Randy V

That additional information tends to confirm my suggested corrective action, Rick.

dr bob

Just to add some more to this discussion, and undoubtedly cause some more confusion:

The pad sensor is a little loop of wire embedded in the phenolic/plastic block. As the pad wears down to the block, the rotor wears away the plastic and then the wire itself. Once the wire is worn away enough, the circuit to the warning module OPENS, and the warning is displayed.

The sensor cable attaches to the rest of the car at a plug connector that's supposed to be attached to the suspension near the caliper. That cable can grow weary with age and flexing, or the connector itself might be dirty, giving the false reading.

Because the problem appears when you turn, it might be safe to focus on the front wheels first when troubleshooting. While there are a few places that can have a broken wire or a broken circuit, the fix will probably still be a new sensor. So, buy a new front sensor, and just plug it in to the sensor plug on one of the front wheels. Tie the sensor itself to the plug clip with a couple wire ties so it won't get damaged, and tie the old sensor wire up the same way. Go drive as you did before, trying to cause the warning to appear this time. If it goes away with the new sensor on that wheel, you just need to pry the old sensor out of the pad there and install the new one in its place. If that wheel isn't the place for the cure, do the same trick on the other side. Then it's on to the rears if you still have the problem.

My luck has it that the last sensor I try will turn out to be the problem. I guess that's because I fixed the problem.... But it gets better! You have a 50% chance of getting it right, and a 100% chance of getting it wrong when there are two possible choices.


Good luck! The system is simple, and we are undoubtedly smarter than it is.


Cheers--

dr bob


--

Randy V

Hmmm, not sure as my real-world experience jibes with yours Bob.

I have reused pad sensors in the past that have worn down to the 'Pad Warning' point - just reinstalled 'em without any further 'Warning' lights showing.

Additionally, when they had first worn down, the "Pad Warning' indicator did not come on until the brakes were applied (warning light off when brake pressure released) - further reinforcing my notion that the sensor is normally Open, until they short out on the rotor.

I could be wrong though - wouldn't be the first time (since lunch).

Paul D

Randy V - I think Dr. Bob is correct. I had a brake pad warning light on my dash and decided to remove the brake sensors altogether (I'd rather rely on my visual inspection which I do frequently as I'm sure many 928 owners do). I added jumper wires across the terminal connections and the warning light went away. As long as there is a conductive path between the 2 terminals on each brake pad sensor there will be no warning light generated.

Randy V

Well, there ya go - I'm outgunned on this one. Thanks for setting me straight Paul.