PSM question

Over here in Iowa we have our first batch of long-lived snow and ice. I've been having fun demonstrating what antilock breaks and PSM do for friends. Something occurred to me about PSM that I wanted to check here. Is it true that your foot has to be on the gas for PSM to engage? I've been trying to get it to engage without my foot on the gas, but haven't had any luck so far. It really does an amazing job at keeping me going where the wheel is pointed when slipping around. Given how likely it is that I'll really "need" it at some point on an Iowa winter road, I guess I ought to keep it in mind that the gas is needed for it to engage, if that's the case.

traction Control only works when you have your foot on the gas, obviously, but PSM can brake various wheel combinations to straighten out a spin, most often when you lift or brake in a turn, lost rear traction, and begin the inevitable....

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

But i have watched it correct cars that were braking on the track. And, oddly, the brake lights do nto come on, yet its obviously braking and twitching like a flopping beached fish :-)

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Supposedly the brake lights "strobe" when ABS is activated. I haven't seen it occur (for an obvious reason!)

Minus 40 degrees... Is that Fahrenheit or Celsius?

For my car at least, I've tried to get it to engage while sliding without gas. The test is relatively easy to do with snowy roads. So far, I've never managed to get it to engage without my foot on the gas. I think I've actually been doing this without both gas and brake (induce a slide, lift both feet and steer in a direction that the car isn't going...no light and no noticeable correction). I'll try tomorrow with just the brake, but that might require a bigger parking lot

Porsche's description (for Cayenne's, and I assume the same as other cars, [www.porsche.com]) says that if you are braking very stiffly due to emergency, it will use PSM to maximize all four of the brakes. They also say that if you very suddenly release the throttle, it will lightly engage all four brakes in anticipation of an urgent need for them. The rest of their description sounds like it only engages when you are giving at least some throttle.

As I understand stability management (Porsche's or anyone's), it works by monitoring each wheel's rate of rotation and correlating that to the position of the steering wheel. If there's a "disconnect", then ABS-like action is taken on wheels at opposite corners of the car to counter the detected instability.

It doesn't seem that throttle state should have anything to do with the need to apply PSM action... although I would not be at all surprised if throttle gets automatically cut during the correction...

Right, that's what I understood as well. The porsche description does say that it can cut throttle if needed. Maybe the indicator on the dash only pops up when it does that, and it could be engaging at other times just without my knowing it. Still, I think a lot more donut-like maneuvers in the local big box parking lots are in order for me to properly understand it. My girlfriend has a mercedes with 4matic, and I think some kind of stability control as well. I think we need to test that one too, just for completeness