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Old 08-06-2010, 04:30 PM   #1
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PSM & ABS Light coming on intermittently

Hello Friends, The yellow ABS & PSM lights on the dash have started coming on TOGETHER intermittently ,they go off when the car is turned off and back on, and can stay off for the rest of the journey ,only to come on again the next mid -journey??? Any Ideas Folks ? THANKS
BOXSTER 3.2 S

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Old 08-06-2010, 04:32 PM   #2
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Have you checked your brake fluid? Pad thickness?
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Old 08-06-2010, 04:56 PM   #3
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I believe an alternator going bad can trigger those warning lights.
My ABS light came on when my alternator was failing. I replaced the alternator and everything was fine.

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mike
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Old 08-14-2010, 02:46 PM   #4
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Pads ok ,fluid level ok . these 2 lights always come on Together at the same time, sometimes they dont come on at all.My ABS is working fine when i slam the brakes on .The PSM switch works fine and illuminates when pressed(untill the warning lights come on ) What about Tyre pressures ? is there a system that detects a Tyre down on pressure then lights these 2 up ?

Just a thought, but how come there are no Porsche Mechanics on this forum?
God, you sure would be welcome !!!
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Old 08-14-2010, 04:17 PM   #5
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Alternator

Its the Alternator - low battery voltage. Same symptoms happened to me last week on my 01S, with a bad alternator voltage regulator. Battery voltage went down to 10.6v. I had a similar experience with my '86 Mercedes, with the ABS light on, but not the battery light. Bosch apparently still can't get the battery light to be more sensitive to low voltage than the ABS / PSM lights. Check the battery voltage before driving again - it should be in the 12.2 - 12.8 volt range when not running.
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Old 08-15-2010, 12:39 PM   #6
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Quote:
Originally Posted by z281974
Its the Alternator - low battery voltage. Same symptoms happened to me last week on my 01S, with a bad alternator voltage regulator. Battery voltage went down to 10.6v. I had a similar experience with my '86 Mercedes, with the ABS light on, but not the battery light. Bosch apparently still can't get the battery light to be more sensitive to low voltage than the ABS / PSM lights. Check the battery voltage before driving again - it should be in the 12.2 - 12.8 volt range when not running.
Thanks for your help,

Are you saying it IS the alternator or it might be the Battery ?
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Old 08-15-2010, 12:45 PM   #7
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So I need to have the battery checked first ? If thats ok then its the alternator ?

I have recently topped up the battery fluid levels, could that have any impact ?
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Old 08-17-2010, 11:56 AM   #8
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I Have trickle charged the battery for 12 hours, the charger indicated that the battery was 100% charged. Drove for 1km, and both PSM and ABS lights came on.
The car runs fine,never cuts out, ABS works , the the light on the PSM switch itself doesnt come on on its own ,only the dash warning light and always at the same time as the ABS light. Can this be EITHER the battery or the Alternator?
I appreciate all advice as I am not a mechanic. Thanks
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Old 08-17-2010, 02:42 PM   #9
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I have the same problem on my '03 Carrera 4S right now. I went on a PCA tour last Sunday and drove for ~3 hours before it came on.... Kinda screwy.

I've done some checking and it can be a number of things. Usually something wonky with your brakes/brake lights. My third brake light wasn't working right, so I fixed that, but that still didn't solve the problem. I'm going to check my battery next as I know my alternator is doing fine since the 911 has a voltage gauge. I think my battery is original (7 years old), so it's probably due for replacement or I may just swap in the battery from my Box to see if that fixes it.

The number one cause of this problem that I've seen on other forum discussions though is a bad brake light switch. That's an easy one for you to check. Have a friend push the brake pedal down (or do what I do and use a broom handle) and confirm whether or not your brake lights come on. If they don't, then you probably just need to replace the brake light switch.

Kirk
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Old 08-20-2010, 07:33 AM   #10
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Thanks Kirk, I have tested the brake pedal and..... guess what.... No Brake Lights !
Fuse ok, Bulbs ok so looks like your spot on with your diagnosis.

I have had the Battery & Alternator checked as this has been known to cause these lights to come on, and they are both 100%

I am having a new brake switch fitted and will post the results.

Many Thanks , Martin
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Old 08-26-2010, 02:26 PM   #11
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Had new brake switch , Problem solved!! PSM/ABS light no longer coming on.
Hope this Feed will benefit someone in the future, and many thanks to everyone who added their feedback to help me.

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