Pass side wheel lock-up in hard left turns

[tuonor]

I have an '03 996 C4S coupe with 25k miles and a PSM problem. Car recently got new rear ties and was recently aligned (twice, initially by a local tire shop and then afterwards by my dealer).

The issue is in some higher speed left turns, the PSM light (the yellow one on the dash with a triangle shaped icon, NOT the light that says "PSM") flickers and the front passenger side wheel locks. The wheel modulation is as if ABS is cutting in briefly, just enough to throw the car into a half-second of oversteer and un-nerve the driver. The issue is repeatable but it seems to happen only if you're driving the car spiritedly (say 7 or 8/10ths). It has happened in everything from a 30mph tight canyon curve to a 85mph sweeper.

Took it to my local dealership (Bev Hills Porsche) and they say they can't find anything wrong with the car. They are having some trouble replicating the issue because it is happening on canyon roads while the dealership is in the city.

I just had the car serviced 2 months ago, and subsequent to these issues appearing, had the alignment checked and the front wheels cross rotated to make sure it wasn't a wheel issue.

Anyone else had this problem or know what might need to be checked? Reading some other posts it sounds like it could be the steering angle sensor or a wheel speed sensor.

But figured I'd check here before I effectively have to write the dealership a blank check.

Thanks.

[wwest]

Chicken or the egg..??

Left turn, HARD left turn, the rear begins to "kick" out to the right, overstear, PSM will brake the right front wheel to "counter" the overstear.

Assuming the same thing DOESN'T happen in a hard right either the yaw sensor or stearing wheel rotational position sensor is/has failed or is out of calibration.

What happens with PSM OFF..??

Edited June 8, 2009 by wwest

[tuonor]

Chicken or the egg..??

Left turn, HARD left turn, the rear begins to "kick" out to the right, overstear, PSM will brake the right front wheel to "counter" the overstear.

Assuming the same thing DOESN'T happen in a hard right either the yaw sensor or stearing wheel rotational position sensor is/has failed or is out of calibration.

What happens with PSM OFF..??

Thanks for the reply it does not happen in right hand corners. Also not feeling any oversteer initiated before the PSM engages. Doesn't PSM allow a bit of slip angle before interfering?

Will have to try sans PSM.

[A2MVS]

Has anyone got any suggestions about a fix for this problem?

I've got exactly the same problem on my car. It's an '03 C4S UK car (so right hooker) and I've just replaced the rear tyres for Pirelli PZero Rosso N5. The fronts are Continental SportContact2 N2 with 5mm. Do I have to replace my front tyres as well? :huh:

[whall]

The following two paragraphs have been taken from page 201 in the MY03 (US) Carrera Owner's Manual:

"Only tires with the same make and with the

same specification code (e.g. "NO", "Nl"...)

can be mounted.

Tires should be replaced no less than on one axle at

the time.

Only tires of the same make and type must be used.

Mixed tires are not permissible."

There could be a problem with your tyre mix particularly if there is a significant diffrence in tread depth between the two tyre types.

Bill

[tuonor]

Has anyone got any suggestions about a fix for this problem?

I've got exactly the same problem on my car. It's an '03 C4S UK car (so right hooker) and I've just replaced the rear tyres for Pirelli PZero Rosso N5. The fronts are Continental SportContact2 N2 with 5mm. Do I have to replace my front tyres as well? :huh:

Interesting, does it only happen on one side or does it happen on both? Mine are all matching but the rears are new and the fronts prob have 5k miles on them.

[demosan]

Has anyone got any suggestions about a fix for this problem?

I've got exactly the same problem on my car. It's an '03 C4S UK car (so right hooker) and I've just replaced the rear tyres for Pirelli PZero Rosso N5. The fronts are Continental SportContact2 N2 with 5mm. Do I have to replace my front tyres as well? :huh:

Interesting, does it only happen on one side or does it happen on both? Mine are all matching but the rears are new and the fronts prob have 5k miles on them.

tuonor,

Have you tried turning off the PSM under the same driving conditions to see what reaction you get ?? I don't believe your problem is related to tire size issues, but possibly a bad wheel sensor??

demosan

[tuonor]

After having it back in the shop to have the sensors cleaned, the problem persists.

To respond to a prior question that was posted, shutting off the PSM does seem to eliminate the lock-ups so this seems to be a PSM issue.

Is there an easy way to check whether the wheel sensors or steering angle sensors are malfunctioning? The shop that I took it to says that if the wheel sensors were bad I would have a PSM or ABS malfunction light that stays lit in the instrument gauge and this is not the case.

Thanks again,

[wvicary]

The sensor could be electrical sound(not open circuit) but reading a different wheel speed and not trigger a code. Has anyone checked the condition of the wheel brng?

[judgejon]

After having it back in the shop to have the sensors cleaned, the problem persists.

To respond to a prior question that was posted, shutting off the PSM does seem to eliminate the lock-ups so this seems to be a PSM issue.

Is there an easy way to check whether the wheel sensors or steering angle sensors are malfunctioning? The shop that I took it to says that if the wheel sensors were bad I would have a PSM or ABS malfunction light that stays lit in the instrument gauge and this is not the case.

Thanks again,

03 C4S. was this issue ever resolved? I experienced a few psm kick-ins yesteday on hard left curves. I thought that maybe I had come off power too much in the turns, causing this psm to kick-in, but this thread could explain the reason. I haven't been on the same road with the psm off, but will in the near future. thanks in advance, j

[tuonor]

Discovered this weekend that keeping the PSM off does not actually cure the problem...

Its much harder to get the front wheel to lock / pulse but it did happen twice in a 50 mile canyon run. Same situation -- left turns only. Only its much less perceptible with the PSM off.

My guess is whatever is causing this initiates the reaction, then the PSM kick in which makes the problem worse. But given it seems to be initiated with the PSM off, it seems like it is not a wheel sensor problem.

Any other ideas beyond having the wheel bearings checked? Also if I have my mechanic check the wheel bearings anything specific to check for?

Thanks again,

[judgejon]

Discovered this weekend that keeping the PSM off does not actually cure the problem...

Its much harder to get the front wheel to lock / pulse but it did happen twice in a 50 mile canyon run. Same situation -- left turns only. Only its much less perceptible with the PSM off.

My guess is whatever is causing this initiates the reaction, then the PSM kick in which makes the problem worse. But given it seems to be initiated with the PSM off, it seems like it is not a wheel sensor problem.

Any other ideas beyond having the wheel bearings checked? Also if I have my mechanic check the wheel bearings anything specific to check for?

Thanks again,

Tounor, was this ever resolved? Happened to me once today in a tight left. Others?