John McM

I bought my car a few months ago, and this fault has been there from the date of purchase. 2001 996TT with 95,000 miles.

The PSM/ABS is turning off after detecting implausible readings from the left front wheel sensor. The computer readings are consistent about this being the fault.

So far we have cleaned the sensor, checked the wires and terminal, then replaced the sensor, when that didn't fix the fault. The fault trips occassionally, especially on slow tight turns.

Anyone else had the same issues and have suggestions on where to look next. BTW the car has no mods, including intake filters and otherwise runs very nicely.

T2

John,

Same issue here - replaced the left front wheel sensor again (after it had been replaced once already) and also the front drop links (my car has a modified suspension in it) and wah-lah all is well. My car exhibited ABS and PSM lights on and pre-engagement of the ABS (felt in brake pedal) just before the light came on.

I beleive there is a steering wheel angle sensor that also plays into the circuit as well.

Best thing to do is follow the factory troubleshooting procedure and make sure all wires and connections are solid as well as sensors.

Good luck!!

T2

John McM

T2, thanks for the info. I suppose I could swap the two front sensors and see whether that transfers the problem to the other wheel. If that doesn't work, then wiring and connectors are next on the list.

Cheers
John

jpflip

Lately a lot of TT owners have problems with the wires going to the sensor. Continuity will not give you a good diagnostic of the wire condition. The computer reads resistance and if the wire is partially broken you will get continuity but also resistance....

"02996ttx50

^^^ i have also read that slow tight turns are the optimal driving condition for the wires or connections to "crimp", resulting in the cels. i have driveway issues that cause abs/psm cels and i suspect the sensors up front also. i just park differently now, and it doesn't happen.that sounds like a crimped wire or faulty connection to me.

John McM

It's all making sense.

I'm out of the country right now, so unless I get my wife to diagnose the conditions it trips in now, I'm going to have to wait.

Perversely I love fixing these types of faults as it gives me satisfaction and something to share here when I get it sorted. In the meantime, any other experiences would be gratefully received.

"02996ttx50

i am envious a bit. i can count the things on this car i am capable of fixing on my own, on one hand. but i'm convinced that being a devoted reader of these forums has saved me untold dollars in diagnoses and also when i've had to use a porsche dealership for repairs in the past. now a pcar dealer would have to be the only game in town! but i have gained just enough knowledge to not get "f*cked by the service managers. it's kind of a gas to roll up and tell them what to fix and be right, more often than not.

John McM

The Turbo Control Unit in my '93 Turbo 3.6 had a fault. $1,800 to replace the unit, but in the end I fixed it with a $15 relay. My passion is as much about the $ saved as anything else.

I agree that these forums are great for gathering others' experience and saving a few $ or at least having confidence in giving instructions to the mechanics.

Tytus

I was getting the same ABS PSM fault and it turned out to be worn out rear tires and front tires with adequate rubber left. These were stock sized Continentals. The car is very sensitive to tire diameter between front and rear. I bought new rear tires and the faults went away. Check your tires.

Good luck,

Tytus

John McM

Tytus, the rears are very much due for replacement and rhe fronts are ok. It would be great if it was that simple, but I don't understand why the computer would report a problem with the left front wheel sensor.

Was yours giving the same fault message as mine i.e. implausible reading from
Wheel sensor?

Tytus

I don't have wheel sensors so I didn't get that reading. If your rears are worn and fronts are good, that is your problem. I couldn't believe it but that was the case. replace the rears anyway if they are worn and see.

Good luck,

Tytus

John McM

Update: I fitted four new tires and the fault is still there. That eliminates the sensor and tires as both have been replaced.

I anticipated this possibility and have bought a spare wiring harness. An UK supplier had the following on their site:

Porsche 996 ABS / PSM gauge light appears for no apparent reason. ?

One of the the most common problem ABS/PASM light coming on and it says it is the right front sensor with a reading out of range. If you switched the left front and right front sensors and am still getting the same fault code. Next course of action is going to be to replace the wiring going to the sensor since assuming there is a break in the wires or a short.

I will fit the harness and report back.

TheKane

Same issues here. I'm going to check the sensor and wire. I'll post results. I already had them check for faults, and there were none, so the system thinks it needs to turn on, but truly doesn't.

TheKane

I just had the harness and sensor checked/cleaned, and there are no faults visible on the diagnostic. Reading the individual wheel sensor data while driving, and everything looks great. No cutting out of the sensor, and readings right to left and front to back are consistent.

Now I have no idea how to fix the issue....

John McM

Let's hope the new harness solves my problem. I'm still hopeful as the issue is common enough to prompt the explanation and offer on their site.