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!

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.

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.

Having same Problem
 

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.