Brake pad warning light on.

[Bradders59]

As above  - this light has appeared on the dash but from what I can tell the pads and sensors are ok.

I fitted new rear discs and pads last week and had a look at the rear sensors while I was in there. There is a red wire which runs around a groove in the sensor, and presumably when the pads wear past a certain point, the insulation gets worn through which causes the light to come on ?

The wire on both rear sensors was intact, so I checked the fronts and they were both intact too.

So, either I have the wrong end of the stick about how the wear sensors work, or there is another fault in play that I dont know about.

Any ideas appreciated, thanks. 

Edited June 24, 2023 by Bradders59

[cdm]

The sensors form a loop so the light comes on when open circuit. Check you have plugged them in correctly at the strut. Could also be the fluid level low.

 

[edc]

If the light is on,by definition a sensor has triggered it, and therefore it is not ok. You won't be able to reuse that particular sensor. 

[Bradders59]

Bearing in mind the insulation on each sensor is intact, how to work out which one has triggered the light ?

Difference in resistance maybe ?

 

By the way, the light came on long before I changed the rear discs / pads, so I havent disturbed the plugs to cause the problem, as far as I know. 

Pretty sure fluid level is ok, but will check.

Edited June 24, 2023 by Bradders59

[edc]

If your are sure the sensor has worn for the trigger then the fault will be a break further back.

[AMacdonald]

I had this exact fault on my Spanish road trip. All pads were close to the sensors but none were breached. I checked each sensor with a simple multimeter (unplugged each in turn) and one was open circuit - the wire had broken where it enters the plug. I don't think there is a way to identify which one is at fault on a 986 without manually checking them. They are just wires so either the circuit is complete or it's not.

[Bradders59]

Excellent thanks. Will blow the cobwebs of my multimeter and check them again.

I should have thought of checking continuity when I had the wheels off, but hey ho. Lesson learned. Ive never claimed to be an expert . Just an enthusiastic amateur. Lol.

Edited June 24, 2023 by Bradders59

[Bradders59]

Well, I have checked each sensor for continuity and they are all good. Also checked fluid level (although I think that would be a different light ?) and its fine.

Back to the drawing board then. Presumably a break in the loom as none of the sensors are open circuit ?

 

[Crudeoink]

I encountered this light after a track day. The brakes got hot enough to melt the plastic around the sensor wire. Multimeter was showing continuity on all 4 corners but decided to replace them anyways as I picked new sensors up for about £5 per axle! Turns out it was the Rear Right sensor and despite the wire being OK continuity wise, the car wasn't happy (perhaps resistance outside of a threshold?). Anyways was about £11 all in and job done 

[pacificjuha]

I had this issue couple of years back when I started to track the car more. New sensors lasted approx half of the 15 min heat... Then cut the sensor wires to only approx 5cm long and soldered them together per wheel. No more issues at all.

As a disclaimer: I do take the wheels off few times per summer and have made it to a habit on each time to visually check the pad wear.

[Bradders59]

Sounds like the best thing is to just replace the sensors then, and hopefully it will solve the issue.

Thanks to both of you for the info.