Quote:
Originally Posted by JasonIsMyName
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
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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 ?