ABS/PSM warning lights

I have a 2002 996 cabriolet .Recently the ABS/PSM warning lights have been coming on .I have a Durametric tester ordered so I will find out what the concern is.But I was curious the lights come on whenever I hit the brakes ,brake lights work good and I replaced the stop light switch with a porsche part no change .Any one have an idea what is causing this? Its obviously related to the brake light in put .Just curious .Thanks

abs/wheel speed sensor or the hub that it reads it from would be my guess. Did you run over anything or have any suspension work done recently?

No collision of any type, it first came on driving on fwy about 65 mph .I wasn't braking just cruising,over the next couple weeks it happened more often until when ever I hit the brakes the ABS/PSM lights come on .I replaced the stop light switch ,cleaned the MAF no change.I bought the Durametric and should get it tomorow then I can test and monitor the data.I would think if it was a speed sensor the vehicle would have to be moving at least 10-20 mph but this does it while stationary I hope its not the module or the hydraulic unit.I got this car last october and the only things I have done are brakes and oil changes so I will repair it when I diagnose it.I see MAF and stop light switches are common so I tried those .I will post the results .Other than this I love the car .Thanks for your input.

I guess you're sure you replaced the right switch when you did the brake light switch. My car was doing the same thing. I pulled the switch took it apart and cleaned it. When I was re-installing I realized I had been working on the clutch switch. They look identical and are only a few inches apart...

Was your wife or girlfriend in the car with you driving at those speeds? Did she begin to nag repeatedly about being unconfortable or annoyed by the loud exhaust or claiming she will throw up if you don't slow down??? The 2002 was the first year for the mk2 version of the 996 and through research we have found that the car starts to suffer from SAD or "social anxiety disorder". This disorder also leads to alexia when may be the reason the car triggered the PSM light when it thought it was triggering the PMS light (which really doesn't exist). The best thing to do, is take it home and wash and polish it... even vacuum it out. They love vacuums because the constant sound helps to calm their anxiety and promote dopamine. Do this weekly and you'll thank me! Cheers!

I had the same issue trouble shot the abs sensors and everything and the problem ended up being the Break Pedal Switch, replaced it with a new one P/N 99661311302 and the problem went away and never returned.

Nope I am single no PMS b s here ,if girlfriend gets cranky I give her a time out.When PMS strikes there are no warning lights,just the famous "If you don't know why I'm mad ,I'm not going to tell you!"lol. B3freak appreciate the humour,I needed it. Its been a long day . I just got my Durametric stuff five minutes ago going to get it set up and see what I find.I also took the stop lite switch apart before replacing it ,very simple switch .Thanks for the reply .I will post what I find .

Nope I am single no PMS b s here ,if girlfriend gets cranky I give her a time out.When PMS strikes there are no warning lights,just the famous "If you don't know why I'm mad ,I'm not going to tell you!"lol. I just got my Durametric stuff five minutes ago going to get it set up and see what I find.I also took the stop lite switch apart before replacing it ,very simple switch .Thanks for the reply .I will post what I find .

I still bet it is the brake switch. If not, replace the MAF (I think cleaning the MAF rarely works).

Not to be facetious, but have you checked your tire pressures? Don't laugh. When I was driving back to StL from Chattanooga and was about an hour into the trip and WHAM! ABS and PSM lights pop along with the OBC warning. Grabbing my chest to say the least since I just bought the car. Anyway, stopped for gas checked the tire pressures - rears were 10# low and fronts were 5# low. Some have said that is the "comfort" pressures. Porsches early TPMS system, LOL.

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I had the same symptoms......... would happen if I accelerated abruptly at highway speeds. Pulled the codes, replaced the MAF......... problem gone.

Thanks for all the replies and suggestions ,I am setting up my Durametric program now .I use a digital tire pressure guage ,tire pressures are within one pound of specs.I know the MAF can cause a concern because its basically a load sensor .I can start the car hit the brake pedal immediately and the warning lights come on.Brake lights work ,all bulbs good.I am a retired senior master in diesel and gas from domestic car company.With over thirty years dealer experience ,so I understand the elect noise ,loads etc.I should have this tested today ,if my rottweiler lets me.She likes to help but won't fit in this car.

I ran a test using the Durametric and got two codes that when cleared came right back after road testing . P0571,4340 ,both stop light circuit codes.I tested the switch ,a new one I just installed ,and it operated normally.That tells me I have a wiring concern or possibly a module concern.I will test the harness this week and post what I found ,maybe it will help others.I always hate to replace stuff without verifying its operation like I did with the stop light switch.I kept the old one also.

You can do some measurements on the switch end with it installed but unplugged: When brake is NOT pressed: - pin 1 and pin 4 should have continuity - pin 1 and pin 2 should be OPEN When brake is pressed: - pin 1 and pin 4 should be OPEN - pin 1 and pin 2 should have continuity If the above check out, the switch is good and your problem is likely in the two wires between the switch and the PSM/ABS module.

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How do you have all this knowledge?! I'm continuously amazed about the depth of knowledge you have about these cars. Wow. Thank god you're lurking in this forum. Helpful for all members here.

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Thanks! I read a lot of factory diagnostic and technical material but in this case it's real easy. The brake light switch is just a single SPDT switch and anyone can see clearly how it's connected in the wiring diagram.

Well looks like I had a defective switch ,got another one seems to work in garage ,haven't road tested it yet .Will do that later today . I bought the porsche one instead of the aftermarket .Just goes to show that any parts manufacturer can make parts that are inoperative out of the package.It's been an expensive week for me so this is a relief to me.Thanks guys I appreciate all the suggestions ,especially you Ahsai i have a shop manual on cd but couldnt find the the info you gave me.I don't have all the other shop manuals for my 2002.I have put about 15,000 miles on it since my purchase last october.The only other things I have done are brakes and rotors,a few cosmetic items.It has been my daily driver and it's a nice car.Got it from an ex rennlist member that I have'nt seem posting for awhile ,he took care of it. '

Glad to help! The info I gave you wasn't in any manual. I came up with that by myself based on how the whole circuit works. This switch needs adjustments and if adjusted wrong, it won't work. That's why it makes sense to test it with it installed as opposed to bench testing it. That way, you test the adjustment at the same time. Anyway, I really hope that's it.

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Ahsai, you have my vote for an honorary doctorate in technical excellence. You are the RL Porsche Gandhi! ;-)

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Porsche Gandhi LoL I like that!

In my '99, the ABS/PSM light was being triggered in low voltage/low current situations; I believe it was being exacerbated by my failing starter. Since reverting to a stock crank pulley and replacing the starter, I have not seen the ABS/PSM light.

I road tested my car to PCH to Kanan what a nice day ,worked great ,no problems,no warning lights.I bought the part from porsche , got an exchange for defective one. Thanks to every ones input . .

Battery is becoming marginal. ABS/PSM pump motor often switches on with brake application, heavy, HEAVY, motor startup load on the battery.... Try cleaning/burnishing the battery posts/connections first.

Hi had psm / abs lights come up and car running rough and went into limp home mode. Plugged in obd reader and it threw up 7 codes including faulry maf sensor and throttle position sensors. I have just acquired the car 1 month ago and have been driving it daily to prove its reliability, with some 1k miles over that period. a long story short. I replaced the rear engine mounts and part of that process involved removing the maf sensor so the airbox could be removed to gain access to the engine mounts. They engine mounts were replaced successfully and the air ox and maf sensor reinstalled. I placed the maf sensor out of the way in the engine bay to eork on the engine mounts, it seems the connectors got dirty (not the maf sensor itsrlf as inside the airbox) and this dirty on the maf ekectrical connector has bern causing this psm / abs fault codes. To fix, i took the maf sensor electrical connect off and cleaner both the male and female parts with wd40 and wiped off with a clean cloth and reinstalled. This gas fixed the issue. No faulty maf sensor just a dirty connector. My engine bay is not dirty but it shows how sensitive this connector is to containimation and engine problems. sinxe cleaning the connector the engine has been runing perfectly with no fault codes in all type of conditions. Fingers crossed of course...