ABS/PSM problem cured

I just thought it might be worth posting this as it may help someone else out at some point. Starting a few weeks ago I had a couple of isolated instances of PSM and ABS failure notification on the dash display followed by the warning lights being lit. I did note that it only happened as I was braking. However, after turning the car off and restarting there was no reoccurrence for a significant period of time. Now I know I should have taken it to a dealer for inspection but as my nearest dealer is at least a two hour drive and the fact that the fault occurred only twice with a significant period between events I put it off until the next time I would be in the area. Well, last weekend I started to wish that I had taken it in as the fault was occurring every time I hit the brakes. Naturally this was a Sunday so there was no chance of getting it looked at that weekend so I decided to investigate further. I drove home and backed into the garage. As I came to a stop I noticed I didn’t have any brake lights. Following a little reading around I came to the conclusion that my brake pedal switch was the most likely culprit for both problems. It was very simple to remove, a quarter turn and it just pulls out the bracket mount. The switch appears to have two functions, one is to actuate the brake lights and the other is to send a “Brakes on” signal probably to the cruise control. I would guess that the ABS/PSM looks for both and if it finds one without the other it triggers a fault – don’t take this as gospel it’s just my speculation. You can check the switch by measuring the resistance across terminals 1&4 then 1&2 as marked on the contacts of the switch. 1&4 should be closed circuit (zero resistance) with the switch depressed and then open circuit once it is released (infinite resistance), while 1&2 works the opposite way around. You should easily be able to tell if it isn’t working correctly because one or both sets of contacts will not change no matter what you do with the switch or it may stick and give inconsistent results. This is what was happening with mine. I then took the switch apart and cleaned it and it did give me brake light operation but would still throw up faults. To cut a long story short I ended up ordering a new switch which I fitted today and I have had no fault signals since and I know my brake lights work. Be careful when refitting the switch though as it has a self adjusting mechanism built into it. Basically the plunger on the switch can ratchet so that the distance to the pedal is always set correctly. Make sure that when you fit the switch the plunger is pulled out as far as it will go, then fit the switch into the bracket with the brake pedal pushed down. Once the switch is in the bracket give it a quarter turn to lock it in then release the pedal and the switch adjustment is automatic. I am planning on visiting my dealer this weekend to get confirmation that everything is as it should be and to get any fault codes in the computer verified and cleared but it would appear that the problem is fixed. A new brake pedal switch is all it needed! For reference my old switch has a part number of 996.613.113.01 but the new switch has a part number of 996.613.113.02 which I would suppose is a later revision.

Location of Switch - Under dash above pedals Switch Detail For reference, the clutch switch mounts in exactly the same way and is much easier to see if you are struggling to see how to remove it from the bracket.

This is a great post, thanks for being so detailed. I had the same problem after replacing the brake booster on my 99 c4. Before I ordered a replacement switch I took out the old switch per the instructions above and "reset" the ratcheting pin by pulling it out. Reinstalled the switch and voila - all is well again. My problem was the switch pin was set to far in and the pedal wasnt hitting it when not applying the brakes, so the brake lights stayed on. This will set off the abs and psm lights after a few miles. Worth a try before ordering a new switch (however the switch is only around 20 bucks shipped). Thanks again for the great photos.

My pleasure! I'm glad it was some help to you.

Great thread, thanks.

Excellent writeup! Having trouble with my brake light switch (02 996) and this writeup and part numbers are exactly what I was looking for. thanks.

Awesome. No problems yet for me but if and when I do my feeble mind *should* be able to recall that this thread exists. I love internet tech forums.

awesomeness. this post just keeps on giving. my 03 had the same problem got the new and improved switch from pelican and no more abs/psm light. thanks dude for the detailed post.

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So one year later and I had no recollection whatsoever of this thread. So much for my feeble mind. Still no problem for me, but maybe I actually *will* remember this thread of it doesn happen?

thanks for the detailed post, i am not even close to mechanically inclined, but i followed your detailed instructions (no volt meter) so just cleaned the contacts, and everything is working fine. This was my first porsche purchase 2001, not even a week old and it failed inspection, i was bummed. Found this post and voila all fixed. Thanks for the detail that even a rookie can fix a 911 brake issue.

Again thanks to the originator of this post. Same damned thing happened to me on my 2000 C2. Bought the switch from Pelican replaced it and fixed the issue. Some things to note on the C2 with Tip, I removed the screw which holds the air vent just to give me a little more room to work. I could not turn the switch with my fingers so I used a long needle nose pliers to free it up. I also could not turn the new switch to get it started so I put it into position and using the pliers pushed forward and then turned it just a bit. I was then able to finish turning it with my fingers. The wire harness should be removed before taking out the switch. Again very easy but I had to use a small flat screw driver to lift the clips, one on each side to release it. The wire harness is keyed so you cannot put it back on wrong. This is an easy fix but expect to climb into the hard to get to space under the steering wheel. Chris

Just wanted to thank the originator and others for this thread. I've had PSM and ABS lights coming on, at first intermittently, then constant. Mechanic read computer codes and said the sensor was bad in the hydraulic pump for the ABS and PSM - and since the sensor is integral to the pump it cost $2700. That's when I started searching the forums. I hadn't noticed my brake lights were malfunctioning, so we checked that and sure enough, they came on only as you depressed the brake and went off when fully depressed. Replaced the switch and problem resolved! Here's link to complete technical article - Pelican Technical Article: Boxster Brake Pedal Switch Replacement / Clutch Pedal Switch Replacement - 986 / 987 As a side note, I actually went to the dealer to get the part since I pass it every day on my way to work. The parts guy isn't real bright and even though I gave him the part number he gave me the wrong part. It ended up being the clutch/switch the technical article mentions. So I just decided to keep it and replace both switches. Ends up the very next morning the car wouldn't start. Put in the clutch switch and the car started right up. The existing switch was loose, so just tightening the screw may have worked, but just replaced anyway since I had the part. For once a mistake turned out to be a good one!

My wife had the same problem w/ her 2006 Carrera w/ Tip. That switch went out within 2 months & ~ 1,000 miles of ownership. It was replaced by dealer under warranty. My '06 Cab w/six speed failed @ 3 years 11 months & ~ 25,000 miles. It was replaced by dealer under warranty. I checked my records & they both got the part #'s Thanks for the write up I now know how to change it in about 3 years.

I have the same problem. But I still have CPO so I'm taking it to Dealer.

Thanks for the post. I've been fighting with this problem for about a year now. Replaced both front ABS speed sensors, the MAF, and some other bits local Porsche mechanic suggested. It turned out to be the $20 switch all along. 5 minute install and it's working like a champ now. Here's a picture of the package and the old part. The only tricky part of the install is access to twist the new part in if you have big hands. It's not very difficult though.

Thanks very much for the post. First I noted both ABS and PSM lights aglow. Then I noted lack of ABS under braking - rear wheel lockup and smoking. Then I got pulled over by police for brake lights not working. Then I found this post. Now I need to obtain replacement switch. 2001 C4.

Has anyone ever noticed when doing a brake job, under normal braking or even track braking, which, if either set, front or rear brake pads, wear out more than the other? I just did a brake job on my 1999 C2 996 and only needed to replace the rear brake pads. Just wondered if this was normal. Can anyone shed light on this subject. Thanks.

I had the same problem with the PSM ABS warning lights. After a few $100's to my mechanic I noticed that the lights will come only after I released the brake pedal. Well, the $20 switch from the dealer di it. Eventhough it is an original Porsche switch it is little dificult to install but with some filing with a nail file should be no poblem.

I'm having a problem and think the brake switch is at fault...but not sure. I have the ABS/PSM lights showing up on the dash. When the headlights are turned off, my brake lights function normally. When the headlights are turned on, the brake lights do not turn on. Would a faulty brake switch be the cause of this or could it be something else? One more thing...I don't get the ABS/PSM error if the headlight switch is off. Only when I turn it on does the error show up.

Aha! I'm getting the ABS PSM error which was discussed here and, as expected, I completely forgot about this thread. Fortunately it was the first hit when I Googled the error so here I am (again). In my case the error throws when I'm just driving down the road minding my own business rather than during or after I use my brakes. Furthermore - I've just completed a comprehensive brake service where I replaced my brake servo, my rotors, and pads....and a steering rack. Lots of opportunity to knock or foul sensors which is what I was thinking was my problem until I hit this thread (again). After reading this thread I remembered that while I was replacing my brake servo I removed the bracket which fixes in place the push rod from the brake pedal to the back of the servo. Seems like maybe I might have dislodged the switch when I did this. I'm at work now so can't crawl under the dash to check. I did however ask a workmate to help me check my brake lights and lo and behold my right side brake light is out. So.... step one is replace that bulb. I hope that makes the error go away. step two is check to see if the switch has been dislodged or if the plunger is maladjusted. step three is remove the switch and check the electrics and the operation. step four is check the sensors at the wheels for external damage and clean the connections at the pigtails. step four is check the wiring harness at the ABS valve and the ABS pump. I'll report back.

Follow up. I replaced both the rear brake light bulbs. The error disappeared and hasn't come back. Kind of overkill to throw a serious error like that (drive to workshop ?!?) for a burned out brake light but at least we have the internet to help us along. I knew this thread would come in handy. Saved me jacking up the car, taking off the wheels and removing and cleaning the ABS sensors...which is what I was going to do.

Update - the codes did come back. I removed, exercised, and reinstalled the switch. Seemed normal to me. I also removed and cleaned my MAF sensor. Internet says this is a not-uncommon cause for ABSPSM errors (not clear why). So far so good, but we'll give it a few days before I say I've fixed it.

update - the codes never did come back. Plus which I borrowed a code scanner and no codes were stored. Given my symptoms (lights came on shortly after warm up and never while I was working the brakes) I reckon it was the MAF that was the problem and not the brake switch. No harm no foul. Car is working great.

Had the same problem with mine, the brake switch connector wasn't making a good connection. Simply unplugging and plugging back in fixed it, Happens from time to time due to vibration and shock.

Great info. Solved my problem. I have found that adjustment is necessary in order for the switch to work properly. In the brake switch plunger, there are a series of clicks if you pull out the plunger or push it in. If you are on the wrong click when you install, it will not work correctly. I think the plunger clicks wear out to make the switch not work properly.

Stunning posts - esp original asnswer! My PSM/ABS lights on once a week or so Stop / start car - all is well Shall install new brake switch and feedback Imagine driving along and not realising your brake lights are not working! Cheers all Statham

Interestingly enough, mine was a bad battery. The previous owner had not driven the car much and I never drove it long enough for the alternator to charge the the battery. I played around with the brake light switch but no go. It wasn't until I noticed that I would turn the head lights on, the ABS and PSM fault were disabled and threw the 4460 fault code. I threw on the battery charger and let it charge over night. The battery was originally only at 12.0v which I felt was a little low. It's been 2 weeks since I charged the battery and so far, so good! P.S. - A brake fluid flush was due so I had that done and taken care of. Brakes are much better now!

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I am having the exact same problem with my 2004 996. What was the remedy to you problem?

I found the problem with my car. A broken terminal in the tail light socket. Installed a new wiring harness and now she is back to good.

This is a great post...thanks to all who have contributed!! I have a 2004 996 C4S, and after my 1st lap at autocross yesterday, my ABS failure and PSM failure - Drive to Workshop message came on when I braked hard at the end of the lap. The brakes seemed to work fine, and my mechanic said it should be fine until Monday, so I went on a planned drive today. A motorcyclist came up beside me to tell me I had no brake lights. So, I pulled over, verified, and then looked at my fuses. Sure enough, "Brake light/cruise control" fuse had blown. After replacing, my ABS/PSM lights went away. I will have my mechanic check it out still to be sure, but my symptom was fixed with that fuse. Good to have all this additional info, though. Sounds like the cause still may be something else. Odd for the fuse to have blown without some other issue. Thanks, again, for all the contributions...I'll update after I get it back from a checkup Tuesday. **EDIT: My local Porsche expert put it on the OBDII and didn't see anything else wrong...cleared the codes, and still clear a week and 400 miles later (about half of which were pushing hard through the twisties) Whew!

Just wanted to update everyone that it was my brake light switch. I finally got around to changing it with a brand new switch. The new switches do not have the "click" adjustments.

@jwetering - which of your steps fixed the problem? My 2001 C2 has the same symptoms, plus it only starts 1 time in 3 so I think the clutch switch is bad too.

I have the same problem and have not been able to solve it ye. Both lights go on after about 2 or 3 miles whether I use the brake or not. Switch has been replaced twice already and the brake lights work fine. Any ideas ?

I replaced my ABS/PSM pump switch, clutch pedal switch, ignition switch, brake pedal switch (3 times), checked all the light bulbs and still got the lights coming on within a few miles of driving. Neither Porsche nor a specialist could fix it without quoting many thousands. Durametric always gave 'stop light switch fault'. Possibly my car has a wiring fault, but I just sold it with the fault, it was too annoying for me

Holy crap what bad memory I have..... I had the ABS warning come up today and while I immediately remembered that the pedal switch is a common cause I also completely forgot that I had dealt with the error in the past (and documented here). In my mind I had never touched the switch before, but reading here I see that I actually removed it, reset it, and reinstalled it some 4 years ago. This time around I just drove to the nearest Porsche dealership and bought a new one for $30. Installed it and.....so far so good, no more error code.

I was contacted by the new owner after I sold my car, apparently the 4th new brake switch fixed the issue permanently. I must have got 3 bad switches in a row. At least the Durametric was correct and telling me the actual fault.

What is the secret to twisting the switch when you reinstall the new switch? Way too much torque is required in too small a space.

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I put a little dab of oil from my dipstick on the tabs. I was in the field otherwise I would have used a small dab of grease.

Thanks. That helped. I also ended up reaching in with my right hand to twist it from outside the car. I had been upside down so I could see what I was doing.

I replaced the switch for the brake pedal, and as soon as I started the car, the lights were back on. I have been having this problem with the ABS/PSM for about 2 years intermittently, there is no real reason for them to come on, I will be just driving down the road and they come on out of the blue, other times, it seems like if I hit a bump that will trigger them to come on. I have found a burned out bulb, checked over the rest of the wiring in the tail/brake lights, and it all seems good, not sure what my next move here is, and if anyone else has had this problem intermittently what their final solution was. Maybe it is just a bad switch again, the new one has the pin that clicks down, and someone else said the new one dont have that anymore. Thanks.

Hi Guys: I just got the code 4340 shortly after switching to LED lights, to include the third brake light on the spoiler and the rear glass. I've ordered a new switch considering that they're affordable and my car is 92K miles already. My brake lights work just fine, just the codes show even when I reset them. Anybody else running LEDs? If the switch doesn't fix the issue, next step would be to switch back to incandescent lights. I'll update with the result.

Incredibly, 12 years later, still a useful awesome post. Thanks mate. Looking forward for the job tomorrow :-)

Update: I know is an old post but, just as it did for me, somebody will find it useful. It was the LED lights. In summary, replaced the brake light switch (although the old one tested fine) and the problem continued. Just to test, I replaced the third brake lights back to the incandescent bulbs, reset the code and it has not come back. I also found some non-Porsche related posts in another forum about similar problems and describes a fix using a 50W 30A resistor inline with the third stop light or one of the main stop lights. Seems like older car with CAN bus suffer from this. Maybe the ABS computer is expecting a specific draw in power from the stop lights and throws an error code when the draw is lower than expected. For now, I went back to replacing the third brake light bulbs back to incandescent while leaving the rest on LED. I ordered an inline 50W30A resistor (very cheap on Amazon) and will test the fix when it gets here. Hope it helps the next guy down the line. Regards,

The gift that keeps on giving! Pleased this and the subsequent posts have been so helpful.

Yes, great topic. I have this problem, ..but I think from another reason : being a lover of *firm* brake pedal feel, I changed the OEM master cylinder (of my 2001 Boxster S, that has PSM) against a TRW (oem supplier) larger one. (used on GT2 and GT3). The results are amazing, just getting the perfect brakes ! (it is true that in the front, I have 350mm floating rotors and 6 piston monobloc calipers). Well, since the change of the master cylinder, I have a lot of "4460" with ABS And PSM lights on. Some time I'm free of these for 100 miles or so, hoping for cure, but... no, lights come back ! There are plenty of theory on that, where the big MC do not have the same fluid circuit than the OEM MC. This may be one of the reason, i.e.: building up too much fluid pressure ..too early. I want to revisit the switch problem (for sure, I did make that change). But the one that I got, do not have the plunger "clicks" adjustment. I still tend to think that yes, the problem is having too much pressure too early (btw, this is what makes the super great feeling of the brakes), but I think that what generates the PSM and ABS lights on (error 4460) is the difference on the timing between the reading of the pressure sensor (on the PSM pump assembly) ..and the Brake stop switch ! I.e.: if in the brake pedal travel, you have a certain level of pressure to close, ..or earlier than the brake on switch, .. then you got it. I think one way is to have one of those brake pedal switch that has the clicks adjustment, or, may be a kind of Teflon spacer between to top of the switch and the pedal space that touch the switch, this to have the brake switch on a bit earlier. I did not had time to work on this yet, but I'm going to try. Some guys on other forums think that the big MC built too much pressure, but frankly, I do not think so. I would imagine that one that brake REAL hard, with the OEM MC of the 986, would also got high pressure, ..but much "later" in the pedal travel distance ! It seems to me that what I'm reading here, tend to keep me think that you really need to have Pedal brake on first, ..and later in the pedal travel distance, pressure is building up. If the reverse happen, I get the feeling that this does trigger PSM/ABS error. Sure, if you limit the pressure (adding a pressure limiter in the circuit), you delay the threshold of the PSM pressure sensor, ..and solve the problem. But, I'm for trying to act at the "other end" !! Or, depending on our brakes, ie.: great brake fluid, very well flushed with good thick pads (and rotors !), I would think that a brake switch that is not well adjusted, and tend to go on a bit late, ..can be the real source of the problem. More to come ! ..and thanks again to all of you for the great topic.

Very useful info. Just replace a faulty switch that was not passing correct info to the PASM/ABS but the Brake lights still worked. Was scary driving round corners off the brakes and the ABS kicking in, not nice at all. I made a quick vid to show the expected vs unexpected behaviour when testing resistance with a multimeter. I know its my first post but I'm no youTuber and just thought would be useful for some who prefer moving pictures https://youtu.be/jWU_NCgHiY8

What causes the fault is when the car does not see brake line pressure and switch connectivity at the same (relative) time. Very common problem that you all have found the cure for. A scan tool with live data will help confirm the issue before parts replacement. Cheers

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Very interesting. Recently I noticed the rear brake lights on my 996 C2 Tiptronic were stuck on. I thought this odd because the switch was changed only 2500 miles ago when it was diagnosed by the garage as an issue. Then I started getting an ABS/PSM error warning on the dash. First off occasionally, them more frequently. Errors disappear when you knock off the car and only reappear after some minutes driving. I got out of the car a few times and found the brake lights stuck on. So I suspect its brake switch related and order a new one and fit it. Pig if a job btw. Brake lights now work fine, and I go for a drive. Error messages come up and I let the car stop without using the brakes and find.....brake lights stuck on again!! On investigation the 'ratchet' in the switch 'piston has settled in a position where the brake pedal has stopped ever so slightly away and so the piston doesn't get compressed. I re-extend it. Happens all over again. But now driving with these messages on all the time the car now goes into 'limp' mode and just ticks over. Sometimes brake lights on, sometime not. Engine resumes normal service after a minute or two parked, running. Very disconcerting. So, there being no way to adjust the pedal position or the switch, I make up a 'spacer' on the face if the pedal to ensure it contacts the piston on the switch all the time, to prove a theory. Brake light service resumes as normal and.....5 minutes later ABS/PSM error is back. I've just triple-checked and the brake lights are working as normal, spacer still effective. Now my local mechanic plugged his tester into the car and got error 4340 Brake Switch A Circuit. What function is A as distinct from B ? I'm getting really cheesed off with it at this stage and it's annual inspection is due shortly which it won't pass with this light on. Looking at your video om wondering why your OEM doesn't have the ratchet feature. Is that true of all OEM Porsche switches ?

And another PSM & ABS light alarms......................i bought recently a gt street Techart 996 turbo , ans i have this problem. I replaced the stop light swith pedal , with a Porsche part , no result, Durametric says nothing . ABS sensors ??? I'm going to change the brakes fluid , hoping that could be a solution ...............but there are plenty of possibilities. I'm a bit lost.

Load test your battery; when the battery is on the way out, it will trigger ABS and PSM faults.

Ok , thanks , but but my battery seems to be ok , voltage is good , and Ctek charger always connected.

Load test it................

Also check that MAF. I tore the connector off of my wire recently (long story) and that abs psm light came on straight away. Computer wants to know what's happening at the intake so it can make good psm decisions.

THX mates for all these advices , I'm going to check battery load , and changing MAF in a first time , and will let you know the result.

Some news , I have had my battery load tested , all is ok. I'm going to replace today the mass air sensor , and i will see..............

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I don't think it's expensive to buy a new one, but you may try to inspect and clean the old one first. There is a thin wire drop inside which should be visible. If it is very dirty or broken then that would confirm the problem. Good luck and please do report back.

Mass air sensor changed , stop light switch changed , and still the psm / abs problem. I'm a bit fed up with this problem , I'm going to be obliged to have a real piwi test to check that , and finding exactly where is located the trouble. My durametric pro version says NOTHING , this tool is just ............. ABS sensors , hydraulic pump.................i'll find it , but it's really boring at long.

Next step : i'm going to change the abs hydraulic unit sensor , this could be a solution on my own.

Excellent posts. I have a problem with a 2004 996 C4S. When I turn on the parking lights I get an ABS/PSM error. Diametric indicates P0571 DTC. I went through multiple brake sensor switches that would not fix the problem. Finally had a local indie shop diagnose and they replaced the brake switch and no joy. I don’t think they validated their repair because there’s no change on the condition. Would appreciate solutions from anyone with similar experience. At this point will start looking for parking light connector and bulb issues and then possibly the headlamp dash switch. Not sure that a bad fuse is an issue but easy enough to check.

In your case , on my opinion , it could be a light swith problem , simply.

No news , like durametric permits nothing to identify the problem (or i not found) , i'm going to be obliged asking for a piwis checking. If someone knows how to use durametric for this problem , i listen all advices. Thanks

I must precise that my TT is a Techart GT street , with rear wheels drive only , ans equiped with a lsd differential system. Piwis will be done next week , and i'll know............and let you know as promise.

PROBLEM SOLVED. A friend came with a PIWIS and found a steering angle sensor not calibrated correctly. Battery had been changed previously , and that's the cause. And now , all is ok.