DaveK

I've had this on mine - in fact, I've had it on front right and front left at different times.

It's not the sensor. It's the wiring from the socket that the sensor plugs into up into the loom. You can buy the part, cut the old one out and solder the new part into the loom in the luggage compartment.

Solved my problem both times - although I had false brake pad wear light more than ABS / PSM when it was the RHS (although did get ABS / PSM sometimes too).

John McM

Dave, I bought the harness solution from Design911. It was GBP 71. I hope mine is a plug and play repair. I gather you are doing something slightly different i.e. splicing into the harness rather than replacing it.

Do you have any thoughts as to what is happening to the connector/wiring that degrades and causes this fault?

DaveK

I'm not sure how it can be plug and play. The socket seems to go straight into the loom - I can't see how you can replace it without cutting the wires in the luggage compartment and soldering in the new one - there is nowhere to "plug" the new socket + wiring into.

I don't know what causes it - but it does seem to be a known problem, even though I've never seen it mentioned much on forums. I don't use an OPC - but after it had happened the first time (and been solved) I was in an OPC for a very much overdue safety recall on my 964. We got talking about the fact that I had a 996 turbo as well, and I mentioned the problem I'd had with brake pad wear / ABS / PSM lights coming on. The tech immediately said it was the wiring from the socket, as if he'd seen the issue several times before.

John McM

I'm not home for another two weeks so all I have right now is a picture of the delivered package. I can't make out much though the wrapping. It looks like a reasonably long cable. The part number is genuine Porsche 99661295700. I'll get my wife to take it out of the package and see exactly what's in there.

Do you have the part number for the socket you replaced?

In any case it looks like I'm on the right track.

DaveK

I just checked my paperwork and can't find the receipt for the part - although the place I usually get parts don't seem to print part number on the invoice anyway.

"long cable" makes it sound like the same part I'm talking about though - the cable runs up behind the wheel arch liner, into the luggage compartment and you solder it in there.

John McM

Doh, it appears that i have bought the cable to repair brake pad warnings. The part is a connector and what looks like two wires that will have to be soldered in. I think I'll leave any more updates until I'm in NZ and can see what's what.

DaveK

OK, not sure what that is.

The part I bought (was official porsche part) was the socket that is mounted behind the wheel. It is actually a double socket - one for the brake pad wear sensor to plug into and one for the wheel speed sensor to plug into. From the back of that socket, there are then about half a dozen wires (although covered in a single outer insulation) which can then be soldered in the luggage compartment.

T2

John or Dave,

If I recall correctly the steering angle sensor also plays into the logic for this circuit. I've not yet solved my problem either but that is something I am going to try and change next, my thought is that is the steering angle sensor reads something amiss it is actually sending faulty info to computer and hence the wheel speed sensors are getting bad info and we have been chasing the wrong part. I'm probably going after that this week in my car and will report back also.

T2

John McM

Update. My ABS Pump sprang two leaks and I'm having my wiring harness repair kit fitted at the same time. Fingers crossed that this is the final solution.

FWIW: In my travels I discovered this on the Net. I'll record it here so others have a diagnostic path.

ABS / PSM gauge light appears for no apparent reason.

Possible Causes:
•A wheel came off the ground, wheel hop from accelerating quickly at a low speed, or you hit a pothole (Solution: Turn off the car completely, then turn it back on. The ABS/PSM light will clear itself if this was the case.)
•Failed Brake Sensor (Solution: replace brake sensor approx $20.00)
•Failed or damaged wheel speed sensor (Solution: check datalog codes for left or right sensor failure, swap left and right sensors and see if the failure moves to the opposite side. Replace if code states failure moved to opposite side. Leave sensors alone if code doesn't change.)
•ABS Ring on Axle (Solution: clean the ring)
•Bad Wiring Harness (Testing: Run double 16ga wire from wheel speed sensor directly to ABS box and check for code to clear itself. Solution: Order repair kit and fix harness.)
•Bad ABS Module (This is expensive and should be your last resort. Solution: Repair ABS Module ABS Repair Company

John McM

Fingers crossed it appears that the wiring harness fixed the problem. I will test the old harness to see what is causing this fault.

MK19

I had the same problem and found a fault in the harness at/inside the rubber strain relief where it goes into the bracket at the brake. After cutting it open and troubleshooting it to that point with a soldered spice and a bunch of tape, I then bought the repalcement lower harness for a proper fix.

I considered doing the other side at the same time, but thought I'd wait....and I'm gald I did because its been good for years.

John McM

MK19, I didn't have time to fit the harness repair kit so gave it to my mechanic to fit and am not aware of the various routings. I tried a continuity tester and all read ok. I then tried to move the harness but all wires kept continuity. Where exactly in this photo did you find the crimp?

MK19

The failure occured insdie of the upper most grommet shown in the picture just below the connector. This is where the harness attaces to the wheel carrier and has a lot of bending with steering action.
Sorry.....I couldn't figure out how to inset a pictue.
MK19

John McM

Thanks, I'll cut mine open at that point to see whether mine had the same damage point. My PSM alarm came on when breaking or sharp turning. It all now makes sense. A pity it took this long to find the cause and fix. I hope by documenting it here there will be less pain for others. BTW I see why you fitted the kit even after diagnosis as this is not a repair you can jury rig and have it last.

Kevinmacd

TYTUS - Never got a fault from the sensor due to tires, but did have the PSM kick in on turns when normally it would not. This was a symptom of tires. A fault would be from electriacl feedback of failure, not tires.