I noticed that even with PSM switched off, I still see a flashing light on the dash when spinning the tires. I assume this is the loss of traction indicator, and in my previous cars that also signaled that traction control was activating.

Is there something else that needs to happen to truely turn off traction control, or is this the way it works?

 

No, it's not really off. You have to unplug it at the charge pump in the front boot lid to get rid of it completely.

 

heavychevy, you sound like you know a bit about the workings of this system, could you elaborate more?

With PSM off, my 2002 Carrera still has some "electronic limited slip" function, but no stability aid what so ever, the triangle indicator does flash when it's pulsing the brake on the spinning (inside) rear tire. I've driven and instructed in 996 turbos that didn't feel particularly imposing and they can certainly carry on with much more inside rear wheel spin (VIR North comes to mind).

 

When I switch off PSM on the console I never get interference regardless of conditions. Am I just lucky or should I be worried?

My buddy's 996TT was always the same way. He wrapped it around a lamp post though so I guess maybe I should be worried!

In all seriousness, what are your thoughts on this?

 

This is how it works, the PSM has yaw sensors that have a predetermined amount of slip angle in them. You can drift the car or even spin the car as long as you keep your foot in the gas, but the moment the car is out of shape and you tap the brakes the PSM continues tapping the brakes. It feels as though Porsche put this feature in to keep Porsches from going off the road backwards which was pretty common when the 996 came out. Now it goes off straight forwards. The PSM at this point does not cut power, it just keeps tapping the brake to help straighten the car out. This can be beneficial, and it sometimes cant (IE Trailbraking on the track).


Likewise on the street, if you are going around a corner and get a little sideways and tap the brake, it's hard to tell what's going to happen because the PSM is back on doing stuff.

Conversely, if you are not tapping the brake and the PSM is interupting when you get just regular wheelspin, something is wrong with your PSM. You can completely disable it by disconnecting the charge pump in the boot lid.

 

I guess the modes of operation are different between a two wheel drive Carrera and the Turbo. On the Carrera, PSM stays off no matter what you do, but the "electronic limited slip" function can't be turned off. Unfortunately a mechanical limited slip diff was not an option on the regular Carrera in 2002.

Anyway, when PSM turns itself back on (tapping the brakes under high yaw/lateral acceleration) does the dash light go out as well, or does it just intervene that particular time, but allow another powerslide once you're out of that situation?

 

HC, good info, thanks. This fits with my experience. I was told by a porsche tech friend that our cars with psm off is how the new GT2's and GT3's are(very mild psm). The 996 GT2 has no psm at all in any form.

 

To me it's all PSM if it applies brakes or cuts power electronically. The light does not go off in the Turbo either, it just pulses the brakes until the yaw is gone, but it will keep applying brakes until the car is straight again. So you think PSM is off, but it's still there.


If you go to the track, try a hard trailbrake into a corner and before you get your fott all the way off the brake pedal you'll feel the pedal pulsing up and down on it's own. Thats the PSM. Doesn't happen with the charge pump disconnected.

 

Some PSM systems (I believe the 996 turbo does this as well) also have a feature called ~"active brake diff" which tries to keep both rear wheels turning at nearly the same speed under braking, even with PSM off. The 997.1 GT3 does this as well, though the 997.2 GT3 doesn't seem to. I think all the 997.2 cars have a fully defeatable PSM systems. The 996 turbo's PSM seems very intrusive to me when turned on, but I haven't had it intervene w/it off. I'll be more adventurous with large yaw angles on corner entry if I buy one of my own.

From what I can tell, the "PSM" operation on the 996.2 Carrera (non-turbo Carrera 2 if you will) can be fully defeated, but active brake/active limited slip functions remain. With PSM off, the late 996 Carrera only looks at speed difference between the two rear wheels, and pulses the faster spinning inside rear wheel only. I understand why you'd lump that with all PSM operations, but it is different in that it will not cut power, nor brake more than only one inside rear wheel. This I don't mind on the 996.2 Carrera, as a limited slip diff was not available. That said, yes I'd prefer a proper LSD and fully defeatable systems.

While we're at it, when you say charge pump disconnected, are you referring to an electronic connection, or removing hydraulic lines? I assume pulling the ABS fuse would remove all PSM intervention, but you'd lose ABS along with it. :/
Thanks for all the input btw.

 

It's an electronic connection right under the brake fluid reservoir. And yes you assume correctly, pulling the ABS fuse, costs you ABS too.

I've driven some C2's but I haven't driven them hard enough to know much about their PSM system. All I know is that I can't stand the one on the 996 TT and am sooooo happy with it off. Now I can trailbrake to my hearts content without the car trying to fight me on it.

 

I find that with PSM on, the ECU will cut throttle if I get excessively sideways in my drifting efforts.