ABS/PSM lights on, tried usual remedies

Vehicle is a 2000 C4 Millennium, 99K, that I'm helping a friend with. -Had CEL, PSM, ABS lit up. -New Bosch MAF fixed CEL (and drivability issues) -All lights were off a few drives, then PSM, ABS came back and stayed on. -Replaced brake light bulbs (even on third raised brake light) -Checked Brake fluid and fuses, all good. Is there a relay somewhere? -Brake lights work with headlights on or off so I don't think it's the brake switch -Battery and coils are brand new. Although I haven't been on a long drive lately. -Can I check/clean wheel sensors with wheels on? Other tips? Thanks in advance 06 997S 00 996C4 Millenium Edition #4 Wife's 11 MDX Solely missed 79 targa 89 Saab 900 turbo SPG 83 Saab 900 turbo Sorta missed 99 Saab 9-5 2.3t Wife's 1st generation Miata

Change or at least pop apart the brake light switch and clean it.

If you have durametric, just scan the ABS module for error codes and go from there. Is the MAF the correct one for the car? Any mods on the intake?

Did friend "upgrade" to LED taillights? Does friend have any hard start issues? LED tails that don't have resistor packs can cause this issue. Low voltage due to a dying battery, voltage regulator issues, etc. can also cause the issue. Here's my personal experience with ABS/PSM lights on my '99. * After purchasing ~4 years ago, I saw this exactly one time before moving to LED tails. * After purchasing LED tails, ABS/PSM lights appeared once or twice more. Not enough to assume the resistor packs were bad. * After purchasing and installing an underdrive pulley, ABS/PSM increased in frequency, eventually happening at least once a day. It was at this point I learned that if I put the car on the maintainer every night, there would be no ABS/PSM lights the next day. If I left it off the maintainer, the MIL light issue would resume after a couple of days. * After removing UD pulley, ABS/PSM frequency decreased to once every few days. * After replacing the starter (which was suffering from heat-soak slow starts), ABS/PSM lights have only reappeared a single time - when the car battery suffered a failure and became unable to store a full charge. The combination of a fresh battery, stock crank pulley, and a new starter that doesn't draw the battery down when it is heat soaked appears to have completely eliminated ABS/PSM light combo on my car. The car is still running the same LED taillights with no issues; getting a decent taillight set with a resistor pack matched to the LED load is crucial if you don't want to introduce electrical issues. No other work was performed on the car by me (or anyone else) during this time nor parts replaced; I'm confident that in my case, every occurrence traces back to coincide with a low voltage/insufficent charging situation...

I had the same issue once, then I figured I would try the brake switch since it was available for $10. After pulling the switch part and dissecting it, because it worked fine.. I come to find out the switch had worn contacts, replaced switch and no issues ever again. Hope you are able to solve your discrepancy with out shelling too much cash or tearing too many things apart.

02Z06 and Device 2: Do you mean the brake switch up under the dash by the pedal? Ahsai: I don't have a Durametric, Auto Zone's doesn't read ABS I'm told. MAF is correct and new. I think he had a K&N because I found one with the car. (Friend passed away.) Regular filter is in now, and I cleaned throttle body. No other mods I'm aware of. 5CHN3LL: Tail lights are not LED. No starting issues. I've been trying not to drive it since we are selling it. But the battery is brand new and voltage last night on short drive was 12-14. Should I hook up a tender to it? Thanks all

Yeah, the switch at the pedal. It's easy to clean or replace. I was getting both lights about once a week. Cleaned the switch and it hasn't happened since. That was last year.

Thanks much, will give it a shot. I'll search for a tutorial.

Update: 2000 C4, 99,500 Belonged to friend that passed, I'm helping his wife with it so I don't know full history PSM & ABS lights always on, regardless of ambient or engine temp, headlights on or off. Dealer pulled a 4266 code "Return pump not present." -I've replaced brake lights (not halogen) cleaned contacts. Wiring harness looks good. -New Porsche battery, spark plugs & coils -New Bosch MAF (made huge difference in drivability and fixed CEL light) -Checked ground points hear headlights, they are clean and tight. -Replaced brake switch. OEM from dealer (not fun) -Visually inspected main grounding strap near rear wheel, couldn't turn bolt to clean it. It's way torqued. Weirdness that might matter: -Car loses voltage as I drive. Ended up in low 12s after a 30 minute run. Always starts though. -Rheostat in dash cluster does not work -Door, interior dome, and trunk and frunk lights stay on if doors or hood is open. I think manual says they should turn off after 12 minutes or something. -One headlight is newer than the other and the color of the light seems different. Can't tell if it is because of slight yellowing to plastic housing or different bulbs. Am I missing anything easy? Or is it time to take it in?

Ah.

Hi TX Targa I�m the new proud owner of No.4 :-) Living In Warsaw, Poland, co-managing Porsche Club Poland as a Vice President responsible for classics. Car is in a good hands, now going back to the mint factory condition. Thank you for your recent job and happy to helped Dan�s familly :-) Will keep everybody at Rennlist updated in �Millenium Edition Registry� topic. Best Mike

Do the ABS and PSM lights come on at start up? Or do they come on once you get pass 30mph? Get a Porsche specific OBD scanner to see what Porsche codes it is throwing.

I had similar codes, Mine would return after resetting ECU, finally traced it to Steering position sensor calibration and it hasn't ever came back, Symptoms were previously Left Rear alignment adjust loosened up and I had severe Toe on that side in rear (noticeable looking door car line or directly from rear side. Took it back to Alignment shop after 6 months and Bill Brausnick -Proformance Alignment in Cin OH )checked it and then scheduled me for realignment. (rear takes a special socket to get to nut in a box shape casting). After realignment I re-calibrated steering wheel sensor, found procedure here or RennTech.com. I started at Dead Center, Made a 20 degree turn to right then back to center them then 20 Degree to left. 20-0- 20 Degree makes were made on painters tape on dash pod with school compass. Worked for me and no light return. This was after I tried/tested everything else. Brake switch, MAF sensor, ABS sensors, Hokey/Pokey, etc. I have a write up somewhere else on this board. Good luck. Mike

Regarding the low voltage after driving for awhile, it sounds like you are driving on the battery and the alternator/voltage regulator are bad. Something to check out. Low voltage can make the PMS/ABS light come on.

My '99 C4 has been suffering from this problem so, while the car was in the shop for something completely different, I asked them to take a look at the PSM/ABS issue. I'd recently had the master cylinder and brake booster replaced due to water intrusion and PSM/ABS issue started shortly after that. This was done at a different shop in the NoVA area. I got a call from the service manager today and he claims he has fixed the problem! It appears the brake switch plunger has to be depressed a certain amount before the connection is made. I also found this on PelicanParts:

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Here's a nice walkthrough in case anyone having this problem (ahem... me) wants to try it. https://996outpost.com/viewtopic.php?t=373