Hi Pete trying to follow this out of curiosity, your saying the newer style sensor cant be easily retrofitted. I have a late model 2001 so I don't have that issue but find it interesting.

 

Yes, thats rudskogen.
Did you swap the main ABS-pump unit thats really expensive?

I think the part numbers are listed here.

 

The link above describes this. Its link to workshop manual. Procedure and part numbers includes. I've ordered the parts, will update when work is done and after next trackday.

 

Have you changed your tires...or tire sizes? Do you put "track wheels and tires" on? I had this issues when I put on some drag radials that were not sized properly...car hates that...

 

^Got it thanks - pretty straight forward at least from write up.

 

Have tried with a few different track-tyre setups all at original dimentions and not that much uneven wear. But you experience this on shaking the car, from wrong sizes? How much are your sizes off then?

 

That's about it completely. I was about tho post that myself...

 

The wire harness in the wheel wells from the sensor and brake pad sensors is known to break wires internally.

Bill

 

I have been considdering this but if this was the case here, wouldn't it throw a fault code on the specific sensor where the faulty wheel sensor cable is failing?

 

Sorry to hear of your troubles. Yes, mine did this all the time, but it has become infrequent since the workshop found a code, checked the front loom and reseated one of the front wheel harness connectors. Funnily enough it still faulted a fair bit after that but has since subsided after a tire change.

Mine will still throw a code if I throw it hard enough over a lip turning into a corner to unweight the front but maybe that's just a 'sensor feedback out of expected range' type failure mode where the PSM computer gives up because it doesn't trust the data that came back. Might also be what's behind yours failing if you typically get it when running kerbs.

Over the years I have noticed too that wheel diameters, inflation pressures, and brake fluid level also affect the likelihood of PSM and ABS failing out.

That said, I prefer the car au naturel. PSM and toe in are the primary culprits behind people complaining that the 996 Turbo is unengaging since these throw a big wet blanket over the car's responses. They also slow it down on track, at least with my driving style.

Since it reliably turned itself off within a corner or two on track anyway, I'd usually only manually press the PSM Off button when on the grid for a standing start but I was caught out at one track day a while back when it stayed active and I just wasn't getting the drive out of corners that I needed to haul past someone. When I realised the PSM was still on, I mashed the button so hard that it disappeared behing the dash surround and we passed him within a lap.

What I like about it failing out by itself is that it is truly OFF, since pushing the button only turns it off for acceleration (it still intervenes under brakes).

For me the only downside of PSM failing is that you normally also lose ABS (unmissed personally, even if perhaps a little slower in the wet) and e-proportioning (much missed - the rears don't get enough share of the braking effort) and the e-diff (mixed feelings - it ought to help cornering but also pumps additional heat into the braking system).

Hopefully the above gives you some further lines of enquiry but on a side-note, if anyone here knows how to fully disable PSM without losing e-proportioning (and maybe the e-diff) I'm all ears.

 

Actually I should be fine, looks like 6SO already has the answer here:

https://www.6speedonline.com/forums/...-turbos-4.html

 

EThe 996TT PSM system is incredibly intrusive and makes it virtually impossible to trail brake heavily with any kind of slip angle without having the system go absolutely nuts. It's a huge detriment if you are tracking the car aggressively at anything past 7/10s or so. It makes no difference if you have the PSM OFF or ON as it automatically turns itself ON under braking. The end result is that you end up cooking your rear brakes as the system uses the rear calipers to try to stabilize the car as a slip angle develops. There is no e-diff on these cars, they come with an open diff from the factory. The evolution of PSM in the 997TT system is much better and the 997GT3 better yet as it can be fully turned off.

You can permanently disconnect PSM in about 2 minutes by simply unplugging the connector form the PSM pump. ABS remains intact. You can even install an inline ON/OFF switch for track days if you want to retain PSM for some reason when on the street.

I have completely removed the whole system from the car including the PSM pump, ABS pump, yaw sensor, and all the associated hardware. I run a simple Porsche Motorsport ABS system without interference from anything else. If anyone wants a complete low mileage perfectly functioning 996TT PSM system including the ABS unit and matching yaw sensor, I have one in the box.


[url=https://flic.kr/p/ziy7vf]

 

No. It only intervenes under braking if you step on the brake pedal when the car is sliding. Ie it tries to catch a car that's "out of control".

 

great informative post. i highlighted my biggest complaint but as pete has said, its under hard braking i find. but i'm old enough and foolish enough to believe i'm the better driver without any of it, though when i was new to 996 abs/psm i'm sure it helped prevent on more than a few occasions my driving straight off of a learning curve.

i feel with greater certainty daily, that the removal of the entire abs pump and psm are in my cars future, using pwdrhounds example as a guideline. i cant stand that intrusive fkg stuff. honestly. but i am rwd and its even more of a hindrance now, i feel.

 

Unfortunately it interferes when you are using a slip angle under heavy braking to rotate the car at the apex, the very thing any advanced level driver uses with regularity with the car very much "in control". Once you progress to any kind of higher level of performance driving PSM becomes a hindrance and will make the car slower. Most people would greatly benefit from fully disconnecting the system and taking some DE classes in a controlled environment where the limits of the car can safely be explored allowing one to "feel" the dynamics of the car when pushed toward its limits (which are much higher than what most think). Having PSM disconnected will allow you to more easily uncover a bad suspension set up. Most of these cars are poorly set up with way too much oversteer which makes the cars way too loose (dangerous) at the limit. People complain about the car's tendency to understeer in tight turns while clearly not understanding that rotating the car under braking is the key. Unfortunately this is the very thing that PSM prevents you from doing...