ColorChange

I am having a lot of trouble with the PSM intrusion with my car now that I am on r's. I use trailbraking pretty heavily and try to use it to step the back end out to the correct slip angle pretty early in the turn. I was able to do this with PSM off on street tires and it wouldn't normally intervene. Now with r's, when I do the same thing, PSM often jumps in (PSM "re-engages" even when turned off when you are on the brake at all). Can anyone help?

Bob Rouleau

Tim, my experience with a student's 996TT on R's was that Yaw control intervened. When I tried to trail brake, YC intervened and kicked back hard on the brake pedal. Yaw Control is independent of the PSM switch, i.e., you can't turn it off. Is this what's happening?

Doing some research, I learned that yaw control relies on a yaw sensor and a steering wheel angle sensor. It is calibrated to the tires Porsche specs for the car. It works fine with street tires but with stickier R's the system detects excess lateral Gs and kicks in - quite violently, it really bangs the brake pedal hard.

Rgds,

ColorChange

Bob, that seams like exactly what is happening, just not quite a bang but it really disrupts the car when you wish it wouldn't. I think I am going to try to disable it. I believe it can be done by pulling the fuse (I might lose ABS also).

Bob Rouleau

Tim,

Let me know if you manage to turn it off. I don't know if PSM is fused separately from ABS. Everyone with PSM cars on sticky tires has this problem when trying to trail brake more than a little. Based on my experiment, PSM stays off when turned off but Yaw Control is always on. It isn't a nuisance on street tires, I guess the algorithm is well calibrated to ordinary tires. On R's ..well you found out. It straightened the car out (diagonal braking I suspect) when I was trying to rotate it into a slow corner. Surprised me the first time it happened.

If you figure it out, you will have done a service to a lot of people driving PSM cars on R's.

Best,

bsr_257

My friend Mark LoPilato runs a 996TT in Speed GT World Challenge. They were able to overcome this problem by pulling the fuse. Although the ABS light comes on, it is still active (tip courtesy of Loles/Farnbacher).

-Noby

Nordschleife

I can confirm the Stability Management and ABS are on separate circuits. However, if you turn off the ABS, the Stability Management won't work.
Some EGas cars need their ECUs reprogrammed not to cut gas when you are braking at the same time.

R+C

924RACR

Or pull the steering angle sensor - you'll keep ABS, just disable ESP and TCS (unless the system is vastly different than I work with - it's Bosch, right?).

Jarez Mifkin

I had this same issue two weekends ago in a '02 C4 Cab. I was on street tires and it happened when I was left foot braking. It was very freaky. I was about to start a thread on this, thanks for the info guys!

Nordschleife

Vaughan
If I pull the steering angle sensor, will that not disable some of the ABS functionality? The latest iterations have got a bit smarter when it comes to steering, or is that all tied up in the ESP sub-system?
R++C

ColorChange

I am going to try to pull the PSM fuse and see how it responds as I would like to keep ABS. I just want to get rid of the sudden diagonal kick it give to the car that is very disconcerting.

kurt M

Can you drive the car throughthe corner in question without needing to rotate the back end? Work well with what you have in hand so to speak.

924RACR

I'd like to respond correctly - but I'm not 100% sure exactly what kind of system you're working with, so can't... though I'd be able to say of our systems that while yes, you can lose some optimal ABS performance without the steering angle sensor - it'll work OK for what we're talking about here. Shouldn't kill ya.

Nordschleife

Vaughan
Thanks, thats what I thought. I wasn't sure whether the whole system would go on the blink. An organisation I knowplaces a couple of switches to allow you to switch out the ABS and ESP separately. But they do insist that you turn the ignition off first., so you have to open the door to get at the switches.

R+C

924RACR

Hrmmmm... not sure I'd agree that you need to turn off the ignition to disable it. Turning on, well yes, to get everything working (mainly traction control), but off, I don't think so... not very robust!

TT Surgeon

The PSM will always come back on once you hit the brakes, designed so it can't be overidden.