CAR:
2006 Cayman S
6 speed
I never turn PSM off on the street. I have zero need to. Even when I'm blasting through the canyons I still leave it on. To my knowledge I've only experienced PSM kick in once when I forgot to turn it off during an autocross run and the car refused to dance.
I commute through a canyon road everyday and just recently experienced the car braking on its own AFTER exiting a turn. The road was already straightened out with no more lateral force and letting off the gas and no brakes. Then immediately the car felt like I just drove through a force field and lasted for 1-2 seconds. This occurred 2 consecutive days. Does this sound like PSM to you guys?
KEY POINTS:
Traveling through a long, mild "S" turn going slightly downhill at speed (not enough to slip and still within the limits of the car)
The car started braking on its own AFTER exiting a turn and going STRAIGHT.
No throttle input or brakes were applied at the time.
Felt like rear brakes only.
Duration 1-2 seconds.
No dash light indication
Only happens on one section of this road.
I've traveled through this road hundreds of times in the same fashion. Never occurred before.
After the 1st incident, I checked all caliper pistons and they all operated smoothly.
Installed new pads and rotors but still continued.
I doubt it matters but the car has JRZ pros, adjustable control arms and 200tw tires. Alignment is good.
Thoughts?
My immediate thought is - what's the G sensor doing? It sounds as if it has some sort of problem. It's located on top of the tunnel (not really a transmission tunnel.. dunno what you'd call it) that runs from the frunk to the engine compartment, right underneath the frame for the radio/heater-control assemblies. Small (4x4x1/2") box, wires going to it.
I'd love to record what it's outputting using something like a
PIWIS
or maybe running a
Foxwell NT710
while doing that section of road. It sounds as if it has difficulty keeping up. I have no idea how it generates signals.. but that's my first thought.
Sounds like it. Usually kills power for that one to two seconds, but I usually get the flashing light. But I’ve had a couple instances where it’s felt like it’s kicked without noticeable lights. But I’m mostly experiencing this in HPDEs and usually happens when I’m trying to slip the rear.
Unfortunately I have no data logging tools (shame on me). I do see the silver box. I'm surprised at how many wires are connected to it!
Have you changed tire sizes lately? I have a seen a few post over the years describing almost exactly the same issue in which the car thinks its slipping so PSM intervenes briefly, and this was also described as happening mostly in a long sweeping turn
This can happen because our cars use staggered wheel/tire diameters, so the front
tires
naturally spin faster than the rears for the same set speed. The
ECU
knows this, but can be tricked however if the tire sizes and front/rear rolling ratio is too far out of bounds from factory settings.
This looks to the
ECU
as if one or more of the
tires
are slipping because its moving too fast relative to the others, so traction control intevevens and applies braking to one of the other wheels to counter the perceived traction loss.
In one of the discussions, this wouldn't happen in normal driving, but only on the track in certain long, high G curves as their setup was right on the edge of what the
ECU
would tolerate, and the track would push things over the edge and trigger the event
Good point. I should've included tire sizes. I run 245/40 front (25.8") and 275/40 rear (26.6"). Been running the same tire spec and brand for years. The rears wear out double the rate of the fronts and never noticed any weird
PCM
issues running them bald.
Well that rules out the
tires
sizes most likley then, although the symptoms are pretty much exactly what is happening to you. Very bizarre
Some good points brought up by
@deilenberger
and ICNU regarding the G sensor which is integral to the PSM, and
@ICNU
about tire sizes. Many previous posts here about how a simple tire replacement throws off alignment, handling, steering feedback, but you ruled that out with your response. And no flashing dash lights is odd when the PSM kicks in.
Only happens in that one spot of your commute? Does your commute take you through AREA 51? lol
Dude... it's funny you say that. It literally felt like I drove through a force field. The first time it happened I froze and thought WTF just happened. Drove through this road hundreds of times and never experienced this. Logic prevailed and thought it was a fluke. Brushed it off. But then it happened again with my senses more alert I realized it was the car 😆
And yes it only occurs in that section. There's 2 sections in this road where I hit the same speed (relatively high) but they differ in lateral transition rate. The first one are long sweepers in "S" pattern and no problems there. The 2nd are shorter "S" patterns with equal speed which means harsher lateral transitions. Maybe the car doesn't like it. But why now all of a sudden? That's the weird thing.
