I'm experiencing a very irritating ABS/PSM fault that only occurs to me on trackdays and is therefor a bit harder to fix.

It usually happens when i ride curbs or something gives the car a little shake.
Here is an example:
When fault is active i have no ABS and no PSM at all.
I can turn the ignition off and on again, and everything seems fine, until next time. It doesnt matter if its right or left turn when i ride the curbs, and it can also happen as i brake very hard straight ahead on a little rough surface.

I have not been able to run diagnose with the fault active, but after getting home there is still a p4420 fault code stored.

As far as I know the sensors doesn't need cleaning, and all the sensor-plugs seems to be in good shape. If i had a bad wheel speed sensor it should give a fault code, shouldn't it?

The fault code 4420 points to sensor 996.606.147.00, called "abs sensor" or "rate of turn sensor". Could this sensor fail due to vibrations?
I have read this thread: https://www.6speedonline.com/forums/...-turbos-4.html and there is certainly some mysticism around theese ABS/PSM symstems combined with trackday-use, but i dont think overheating is my problem. Not sure though.

Any thoughts before I go ahead and fork out money for a new "rate of turn sensor"?

 

What model year is your car? Are all parts (= ROT sensor and ABS/PSM unit) original?

 

I see the sensor is around $1000 so I would see if I could swap in a loaner if at all possible to see if that's the fix= which is my guess. Could try cleaning connection?

 

You should be able to do some output tests or physical test to see if sensor is in fact bad.

 

^ Good point and if a loaner isn't available would be the way go.

 

Have you done a good pressure test.

 

Hmm. Sound like a good idea to perform some tests. How would you go about doing this?

I don't think i can get hold of a loaner, but i can get a 2nd hand one for a price i can live with. However that's new part number so i also need a harness adapter and changing all the mounting brackets. New part is probably improved over the old part, as porsche did change it within the first few months of production. My car is very early turbo, produced summer 2000 i think, and all parts are the standard parts except brake fluid and pads.

 

This may be a little out there... Do you run race fuel and could it be messing up your MAF? The MAF will do some crazy stuff.

 

Thanks for input about MAF. I've thought about the MAF being a source for fault since it's trolling a lot on many cars. However I don't think it MAF on my car. My thoughts on why not MAF:

I run 98 octane street fuel on a very mild tune. The fault doesn't typically come on at throttle, but rather more typically on vibrations, riding curbs etc. The 4420 fault code is not MAF related either. Its hard to dial out MAF as its a source for so much, but if it was MAF, should it not happen on throttle?

 

Once again: What model year is your car? Are all parts (= ROT sensor and ABS/PSM unit) original ones? What about brake calipers and master cylinder?

 

As described above the car is produced summer 2000 (model year 2001) and all the parts in mention are stock/original other than brake pads and brake fluid - as far as I know. I don't have complete history on all that's done for previous owners. The car was actually registered 20th of june year 2000 so it has to be one of the first turbos?

The fault have been there for the 3 years i have had the car, but I don't track it often. Between the track-days I have tried different wheel sets, cleaning wheel sensors and rings. I would believe that if it was a fault with major brake-system components it would fail under braking. I would also believe that if one wheel sensor was bad(worn out) it would happen on the road as well. If a wheel sensor was bad, or the wiring to a wheel sensor was bad - I also assume that it would store a fault code on the specific wheel sensor.

Please tell me if I'm jumping to conclusions here.

Are there more brake-system components other than the "rate of turn sensor" that was updated within a few months?

 

With that old, ie early car you most likely have a problem with rate-of-turn sensor. It's most likely one with rubber pads between the sensor and the bracket. New style one doesn't have rubber pads. WSM (WorkShopManual) has instructions about replacing the sensor, including corresponding part numbers. PET has also part numbers. You may find an used sensor from Ebay, as I did.

I had similar issue with that old style sensor, which was coupled to newer ABS/PSM unit. There are programming differences between units and they do not mix, I tried... Street driving is OK, but at bumpy track fault codes pop up and the system disables itself. As a test I removed rubbers from the old sensor's bracket. Needs some work (and tools), but can be done...took about 2 hours few years ago at our hotel's backyard at Adenau... Anyway this way I did not get that particular Pxxxx anymore at the 'Ring. Ie newer ABS/PSM units did not like that more vibrating signal from older sensor/bracket combo. Later I bought an used sensor and a new paired bracket.


BTW, what do you mean by the "rate of turn sensor" that was updated within a few months? Was it replaced, with what and by whom? The reason may lie here, if old one was replaced with wrong unit.

 

I only meant that Porsche replaced it in production(different style) before the end of 2000. August 2000 i think. This would indicate that the old style - witch i have - is no good.

On my car there is still the old style, since mine is produced prior to june 2000, and its never been a swap on my car.

I think I'm going ahead and ordering a 2nd hand new style sensor based on your experience Pete.
Thanks for great help so far. I'll keep you posted.

 

One more question Pete, when you replaced your sensor with the new style sensor, did you have to code anything for the PSM to work?

 

I'll check WSM for instructions and parts, wait few days before buying anything...IIRC you must replave old style one with similar part. I had old style sensor but installed newer ABS/PSM unit. That's when issues at track started.

But back to your question: No, no coding required.

Is that track Rudskog?