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I've been experiencing ABS/PSM problems ever since replacing worn out rear tires and using a different wheels on my MY02 996 C4S manual.

I replaced the rears with exactly the same OEM sized tires, but with different wheels.

Prior to tire/wheel replacement I've never experienced any ABS/PSM issues.

New Sumitomo HRZ-III 295/30-18 at the rear on original C4S solid spoke turbo twist wheels, 11x18.

60% worn Sumitomo HRZ-III 225/40-18 at the front on 996TT hollow spoke turbo twist wheels, 8x18.

Under normal braking in left and right hand turns, ABS or PSM activates causing slight disruption in balance of car. Normally the warning light would just flash on for a second (or not at all). This is fairly repeatable in certain turns, but not others. No problems straight line braking.

Today, after an ABS activation incident, I received an ABS failure and a PSM failure warnings that stayed on. Both warning lights on dash and computer on dash saying to drive to workshop. Drove to safe location, pulled off and parked, turned car off, waited a minute, turned car back on and no warnings.

I know mixing tire brands/models are bad; mixing old and new tires left and right are bad; but is it ok to mix hollow and solid spoke wheels front and back?

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  • Admin

Check your brake lights - a bad brake light switch (on the pedal) can cause both PSM and ABS lights to come on.

If the brake lights come on then it would be best to put a Durametric tester, a PST2, or PIWIS tester on the car and see if there are PSM and/or ABS fault codes.

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Brake lights checked out ok, but left turn signal blinking fast and no rear left turn blinking.

I took out what I believed to be the rear left turn signal bulb (top most bulb in housing unit) to inspect, looked ok. Returned bulb back to original location and reinstalled housing unit. All turn signals (left, right, front and back) and brake lights operating normally.

I'll take to my shop to check for fault codes and report back.


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  • 2 weeks later...
  • 2 weeks later...


I checked fault code with PST2 and found a 4460 event. After reading some other posts regarding this error, I decided to replace the brake light switch sensor (cheap). Drove for a few days without seeing any PSM/ABS faults and thought problem resolved. Unfortunately, this morning I experienced the PSM/ABS activating in usual places again.

I'm going to try judgejon's suggestion and return the orginal worn tires and same wheels to rears and see if that changes anything. Will report back to let everyone know.

While I'm testing the wheel/tire swap, are there any other items that I could check?

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did you get an alignment when the wheels were replaced? Did you calibrate the steering angle sensor? (This will trip both PSM/ABS if not calibrated). I had same problem after alignment when the sensor was not calibrated. Once calibrated you need to clear the computer as well (there's some steps to that on this forum somewhere). I was told I had to replace the angle sensor ($825 new/ $400 from a dismantler). I went through the calibration steps and it hasn't tripped in over 400 miles now so I'm keeping my fingers crossed (it would trip within a minute before).

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  • 2 months later...

dad2n2: thanks for suggestion, but i had no alignment done when wheels were replaced.

Update: so i've swapped back and forth between new and old set of tires/wheel set combinations and it's pretty clear that PSM/ABS issue is related to tire/wheel set.

Although I still cannot come up with a reason why this would happen, I cannot ignore the data and will move tires to common wheel set.

Thanks everyone for their inputs.

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