I have an 02 C4S with the ABS PSM light on. Having read many forums I replaced the brake switch which did nothing. Felt the MAF is probably fine as the car runs perfectly. I bought a Schwaben scanner and found a fault code for the left rear wheel speed sensor. I replaced it and although I have tried to clear it the code re appears without as much as starting or moving the car. I disconnected the right rear one and sure enough the code for it appeared and I was able to clear it once reconnected. I also have LED taillights and they were installed about the time this occurred, I unplugged them but since the schwaben is pointing to the wheel speed sensor my gut says its still in that circuit. I was about to order a replacement kit for the connection to the wheel speed sensor but mice have eaten away at a couple wires elsewhere so i'm wondering if there is a way to test the circuit before I cut into the harness? I was going to try a continuity test but read that doesn't work plus I don't know which pins to use .

 

Wheel sensor Part #5 here http://www.autoatlanta.com/porsche-p...=99660640600#a
I don't think you have to cut the harness to replace the speed sensor, unless the mice chewed up further on the wiring. It by itself is a plug and play sensor.

 

I’ve already replaced the sensor yet still getting the code that’s it’s failed so I suspect the harness leading to it which is a known problem

 

Try doing a "hard reset" on your ECU. Disconnect battery - touch the positive and negative cables together, leave them disconnected for an hour so. See if that does anything to clear your codes (you may have to go through a few start/drive cycles). A few years ago I got a CEL that was related to cam deviation. I did a bunch of engine work that included vario-cam tensioner pads. Upon putting everything back together, the CEL was still illuminated regardless of the deviations now being well within spec. I reset the codes several times, but couldn't get rid of the CEL. Finally, I removed the ECU to check for visible faults on the PCB (which was a possibility according to research I had done) - while I didn't find any obvious faults, I believe the process of removing the board to check it out wound up wiping some sort of stored memory that was causing the code to be continually triggered. Once I put everything back together, the CEL disappeared after about 25 miles of driving, and I never had a problem with it again. Good luck - this stuff can be maddening.

 

When he says "disconnect" the battery he means BOTH terminals. Completely disconnect the battery terminals and then touch the positive and negative leads together.

 

I was about to replace the wiring harness that feeds the wheel sensor on that wheel as I’ve read they are a known problem where they attach to the wheel. Having pulled the seats and carpet to check the wiring prior to ordering one I found a wire chewed


off. Fixed! Yahoo! I had already replaced the brake switch and wheel speed sensor to that wheel. I should have swapped wheel speed sensors prior to buying one but was following the advice of a local Porsche mechanic as he read the code originally. I bought a Schwaben to clear the code myself after replacing the sensor. My suggestion to anyone working on one of these is to buy a code reader before replacing parts that are known to be troublesome. I was worried sick thinking it was my $1k LED lights or worse the ABS pump @ $3K.

 

Agree on buying Scanning device or code Reader, Mine turned out to be Rear Suspension out of alignment, which threw Steering wheel sensor out of spec. One I had it aligned again, I reset Wheel position calibration.

Couldn't have done it w/o durametric.

Only replaced brake switch first....

 

Dang varmints. They do love that wire sheathing don't they. Nice find.