Brake wear idiot light on; sensors removed

[defcon65]

I rebuilt my brakes and removed the wear sensor and wire assemblies. Now the brake wear indicator is on all the time - how do I shut it off? Can I just pull a fuse or disconnect a wire or something?

Thanks for any replies.

[aj88cab]

If you didn't remove the connectors, you can put a jumper across the terminals on the connectors at each wheel and the warning light should go out.

[tonythetarga]

When you say removed the wire assemblies, what do you mean? Did you unplug the wire from the connector in the fender well or did you cut it somewhere? Usually all you need to do is unplug the sensor from the pad and tie wrap it back up and out of the way. No light will come on, no fuse to pull, nada.
I would plug the wire back in and tie wrap out of the way.

[defcon65]

I unplugged all 4 sensors in the wheel wells, shrink-wrapped the connectors and zip-tied them in place. Now the light's on.

[tonythetarga]

plug them back in. just tie wrap the end that would have been connected to the pad. You can shrink wrap the end to keep it from grounding, but that should take care of the light.

[Bill Verburg]

3.2 Carrera use a one wire system that seys the light off when any part of the system is connected to ground. The light is deactiveated by turning the ignition off.

Later cars use a 2 wire system that works differently.

On yours, if the light is activated when you start look for a short to ground.

[defcon65]

I can't imagine it's a short to ground - I wrapped the connectors with electric tape, shrink-wrapped them, clipped them back in the plastic harness holders and installed zip-ties to hold them in place. Do you mean a short in the wire? I'm confused - I thought they were designed to come 'on' when the metal part of the sensor contacts the disc.
I'd hoped there would be an easier solution than undoing all my shrink-wrapped connectors, bridging the wires and putting them back. Can't the circuit be defeated at the instrument light?

[aj88cab]

The Bentley manual shows a loop from the warning light module that "daisy-chains" to all the wear sensors. Perhaps that loop has to be continuous to keep the light off, then ground to the rotor (or breaking the loop) turns the light on. The diagram shows two terminals (#1 & #2) at the warning light module. Try a jumper there.

I change brake pads so often (street/track) that i have not used the wear sensors since I got the car 4 years ago. Fixing this nusiance has always slipped to the bottom of the to-do list. Now I am going to have to do it tonight just to see!

It is always fun to have a DE student get in the car and ask "what's that"? and I reply "Oh, just the brakes, nothing to worry about!"

[Stutzdriver]

Can't one just pull the bulb?

[aj88cab]

Now Jay, why are you trying to simplify things

There's no fun in that!

[defcon65]

It doesn't bug me that much, I just noticed it and thought it might be an easy fix. I feel great about my brakes now, having rebuilt the calipers, replaced the hoses and pads, half of which were worn down past the wear indicator. The previously good braking of the 911 is now unbelievably strong, and it's only the two-piston calipers.

[Bill Verburg]

Originally posted by defcon65
I'm confused - I thought they were designed to come 'on' when the metal part of the sensor contacts the disc.

That's correct, that is a short to ground. It is designed to short when the pad wears, but it can be anywhere in the circuit.

The Bentley manual shows a loop from the warning light module that "daisy-chains" to all the wear sensors

Correct the circuit is fed off theoil pressure light circuit,

It forms a Dual feed loop starting at the RF inner pad next in the series is the LF inner pad next is the LR inner pad and finally the RR. The dual feed comes in at the RR inner pad and goein the reverse direction.

All that is needed to isololate both of the Brn/Blk feeds at the RF and RR pad

[defcon65]

Well, since I just got the car out of the garage for the first time this year, it has not had a chance to bother me much. I'll have to decide which 'fix' is the least troublesome. I'm leaning towards the bulb removal.

[rick-l]

Originally posted by Bill Verburg
All that is needed to isololate both of the Brn/Blk feeds at the RF and RR pad

Can you jumper these two together and see if the light goes out?

I can't imagine they would run two wires to each wheel if all they were looking for was a ground closure.

[Bill Verburg]

Originally posted by rick-l
Can you jumper these two together and see if the light goes out?

I can't imagine they would run two wires to each wheel if all they were looking for was a ground closure.

You don't even need to do that, just disconnect Brn/blk wire which is the feed at the right front and right rear and tape them up.

I suppose it's a sort of fail safe system.

Later cars have a 2 wire system that energises the light when there is a break in the circuit. Just the opposite of the way the 3.2s work.

[aj88cab]

OK, I had a DE this weekend so I was going to change the pads out anyway.....so I pulled the wheels.....

As Bill confirmed there are two conductors to each wheel (i.e., the daisy chain loop - one "in" and one "out").

There is a male and female terminal at the connectors, so to make a good permanent jumper connection you need a jumper with a round female and round male end connector, or install the wear sensors and zip tie them like Tony suggested. For now I just stuffed the jumper in there temporarly.

With the jumpers installed at the wheel connectors the warning light is out. Car must be running to check.

Gound any of the jumper connections and the light goes on. So it needs continuity of the loop to keep the warning light off, and grounding the loop turns it on. If you remove the ground jumper the light stays on until you turn off the car and restart. So there is a "switch" in the module that hold the light on.

So theoretically a jumper at the warning light module terminals would work too. But good luck getting to the back of the module. It is above the radio and cruise control module. Not an easy reach unless you can pull it out from the front, but i am not going to try unless someone knows it can come out from the front without breaking something.

So it looks like Jay wins! Pull the damn bulb

[aj88cab]

Originally posted by Bill Verburg
You don't even need to do that, just disconnect Brn/blk wire which is the feed at the right front and right rear and tape them up.

Bill,

I think I understand that this would work (or maybe not), where would you practically do this? Are you saying to connect the two leads or just disconnect and tape. The two side of the loop go to different wheels. Is there a intermediate connector before the split to the opposite wheels. Some where you have to close the loop. I don't think just disconnecting will do it since the continuity is required to keep the light off.

I should add that this is on an '88 Carrera, it might be different on an '85.....those Porsche engineers are always trying to keep us confused.

Thanks
Andrew

[Wavey]

Originally posted by aj88cab
So it looks like Jay wins! Pull the damn bulb

Actually, the bulb is molded into the lens and isn't replaceable.

I had (have) the same problem with my '88, except I snipped the harnesses closer to the tub, and heat shrinked the ends without them being connected, on the advice of a certain well known Pelican

Now the warning light is permanently on, so I need to go back in and make a connection at each harness. Not a big deal, just haven't gotten around to it. In the mean time a piecce of black tape over the light works wonders.

[Bill Verburg]

Ok, It appears that there is something not mentioned in the shop manual


Apparantly the light is triggered by a short to ground(this is what the manual says) or an open loop(which you guys are reporting.

So a jumper at each pad or at the combination light itelf @ terminal #1 & #2

[arerrac]

I'm at my desk so I can't remember off the top of my head, but doesn't that light also come on if/when the fluid level is low????

-W