I have a theory now.

I tried to adjust the brake light switch, but that procedure just caused two additional faults: Brake Light Switch and Rate-of-Turn Sensor.
So I went and bought a new brake light switch, installed it and all problems are gone! $15-20,- , depending on the source.

Back to the theory, it goes like this: The swich has self adjusting capability with it's built-in ratchet. But as our cars are 10+ years old, the switch doesn't work as designed anymore and causes these faults. New switch resumes correct operation.

 

I had a theory. ABS/PSM warning wiped the floor with it... So during last week I have had that "P4460 Pressure Sensor" Code for at least 5 times. It always comes after the car's been properly warmed up at track (READ: Nordschleife and Spa), after engine start and moving without (or almost without) applying brakes. It's rather annoying (Being there and forced stopping driving prematurely I actually was so ****ed up...) and is clearly connected with that bigger MC. But why?
Here's the revised theory: Somehow that MC is connected to heat induced brake system's pressure increase over some threshold, which causes the code if the car's moved without applying brakes* (=pushing pedal, thus giving the pedal switch signal) after hard track sessions. I had some 500 kms to think about this between Köln and Travemünde, but no chance to test it in that rain...

*Code's thrown if the pressure sensor senses brake system pressure without pedal switch signal. I have a new pedal switch and also readjusted it without improvement.

Any ideas? Anyone? Track season is over, snowfall starts soon, but I wouldn't yet want to switch back to former MC.

 

Over 2 years and 60+ track hours with the complete 997GT3 380/350 brake system including MC, vacuum pump, and brake calipers. No issues whatsoever. Zero... (I have removed PSM however from the very start). I still have the OEM 996TT ABS module and booster fwiw. Brakes are phenomenal...

Pete, your car is a C2. Do you have PSM or some type of stability control that you are running with on your car?? If so, have you tried disconnecting it to see if the problem persists? You don't want it on a track car anyway.. There is also some type of a thrust angle sensor if I recall on these cars that should be adjusted periodicly (according to the Porsche repair manual) but I have never ever done that.

 

My GT2 has no problems with larger MC and obviously no PSM. (Just for more data)

Good luck!
Henry

 

B/c of turbo's Motronic I do have turbo's ABS/PSM unit and all accesories. I haven't had any issues except P5525 caused by MAF faults before installing that bigger MC. Those who have had issues have yet not told what codes they've found.
I might switch back to original MC, but before that I will try another trick, adjusting brake pedal position by altering rod length (that connects the pedal to MC). WSM has instructions for this in the same section where brake pedal switch installation and adjustment is described.

PSM and track car. Well yes and no. On local tracks I do not use it but at (wet) Nordschleife and Spa -like last weekend on both tracks- it's rather nice to have around...

 

Have you tried disconnecting the PSM pump, clearing any existing faults with Durametric, and seeing if anything pops up at that point? That would narrow it down for you.

 

Has anyone sorted this yet? I have a 996 Turbo with 996 GT3 front calipers, 997 Turbo rears, and the 997 Turbo master cylinder. Random PSM and abs lights, sometimes when first driving off, but more usually happening upon the second journey when the engine is restarted.

It has had new brake switch, maf, and brake pressure switch.

 

I recently did this conversion and have no issues at all.

 

Cool, was it exactly as per my spec above?

 

Yes, which calipers F/R and MC exactly? Is PSM in use or deleted? Do you have a new brake light switch? Have you adjusted the brake pedal pushrod length?

 

I've been running the 997GT3 MC, 996GT3 front calipers and 996TT rear calipers without any issues for a couple of years (thanks pwdrhound). The trick is to unplug the PSM and the ABS will work fine. No need for anything else besides rotors, pads and fluid.

 

Different spec then, rear calipers different to mine and I want to retain the PSM.

 

OK, I adjusted the brake pedal pushrod. Obviously to wrong direction, because there was brake pressure without applying the brakes at all. Got the codes immediately when moving, but I also now know that you can only run about 1½ miles before the heat from dragging brakes will cause all four wheels to lock while ABS was already disabled because of the codes. Track pads though, but it will not move before 1 hour cooling period...

So tomorrow I'll try the other direction and see what happens. Now I'm concentrating to single malt.

But back to my revised theory (see above). That bigger MC seems to somehow cause brake pressure increase in the system over the sensor (in PSM) limit when brakes get heated. It's IMO not about the pedal position to the brake light switch (I tried to create less slack) but the MC piston position in the MC itself. The piston should be pulled as far back as possible. Someone should compare 996 turbo's and 997 GT3's MCs by measuring the piston location related to the body and the overall stroke.

EDIT: One should read from the WSM not only the "How to adjust brake pedal" but also "Changing the master cylinder" and "Changing the brake booster". Those parts give more information about pedal's correct position and pushrod length. After readjusting pushrod's length there's now some slack in pedal's movement. Thus it'll trigger the switch before creating brake pressure. I think that this pushrod adjustment is necessary if changing the MC (and booster in my case) to different ones. Test drive will be done tomorrow, but the real test is the first trackday.

 

Rod length adjustment doesn't help. Still the P4460. I'm done, I will change back to 25mm MC.
In addition I will install a switch to completely disable the PSM, but my brakes worked without problems before that 27mm MC.

 

I think you might have jinxed me!!! I just got this error. I'm running larger Brembos gtr brakes front and rear.

Interestingly this is the first time I've had the issue. It also the first time I've had the car moving in hot weather. There could be something to the heat and pressure.

Will report back, but it looks like I'm in the same boat with the larger MC. Shame, I love the brake feel.