Can PSM screw up without throwing a code?

[Dus10R]

Went for a drive today up one of our local curvy roads. Car was great up and most the way back; but then I go into a left hand corner and right about the apex I hear a quiet sound that sounds like I just drove over a small cattle guard, the car instantly starts to understeer and pull to the outside of the corner like a brake was being applied, then it stopped and was fine. Luckily I was driving fairly mellow at the time.

It freaked me out a little because I don't want that happening while the pace is upped, in the middle of a corner. So I drove normal for a little while and didn't feel anything out of place; no codes showing. So I upped my pace a little and get into a corner and it happened again. This time I noticed that it happened right around the same time that I came into contact with some small wash-board type bumps, nothing major at all, you woudn't even notice them normally. So the car lurches, pulls to one side, and slows itself a tad bit. hmmm.

So I turn off PSM, wick up the pace a bit and go through some corners now trying to hit the small bumps and I can't get it to do anything. So I turn PSM back on and hit a few corners aiming for the bumps and it's fine. Then I go around another corner and it did it again.

No fault codes on the dash display at all. So now I'm a little freaked and I don't trust the car. I know that if I take it into Porsche and it doesn't read any fault codes there probably isn't a whole lot they can do. They're not going to go actually drive it at a good pace through corners to duplicate the problem.

Anyone have an Idea what it may be?

Edited July 27, 2008 by Dus10R

[judgejon]

Went for a drive today up one of our local curvy roads. Car was great up and most the way back; but then I go into a left hand corner and right about the apex I hear a quiet sound that sounds like I just drove over a small cattle guard, the car instantly starts to understeer and pull to the outside of the corner like a brake was being applied, then it stopped and was fine. Luckily I was driving fairly mellow at the time.

It freaked me out a little because I don't want that happening while the pace is upped, in the middle of a corner. So I drove normal for a little while and didn't feel anything out of place; no codes showing. So I upped my pace a little and get into a corner and it happened again. This time I noticed that it happened right around the same time that I came into contact with some small wash-board type bumps, nothing major at all, you woudn't even notice them normally. So the car lurches, pulls to one side, and slows itself a tad bit. hmmm.

So I turn off PSM, wick up the pace a bit and go through some corners now trying to hit the small bumps and I can't get it to do anything. So I turn PSM back on and hit a few corners aiming for the bumps and it's fine. Then I go around another corner and it did it again.

No fault codes on the dash display at all. So now I'm a little freaked and I don't trust the car. I know that if I take it into Porsche and it doesn't read any fault codes there probably isn't a whole lot they can do. They're not going to go actually drive it at a good pace through corners to duplicate the problem.

Anyone have an Idea what it may be?

Are you running different brands of tires on front/rear? What you are describing has happened to me since I made the mistake of mixing tire brands. My next pair will depend on whether the front or rear go first. My guess is the rears (RE050's) will go first even tho they are a better wearing tire than the PZero's on the front, which are better traction tires. At that point I'll put on a full set of som'thin.

I'm interested in how your situation resolves. Good luck.

[Dus10R]

Went for a drive today up one of our local curvy roads. Car was great up and most the way back; but then I go into a left hand corner and right about the apex I hear a quiet sound that sounds like I just drove over a small cattle guard, the car instantly starts to understeer and pull to the outside of the corner like a brake was being applied, then it stopped and was fine. Luckily I was driving fairly mellow at the time.

It freaked me out a little because I don't want that happening while the pace is upped, in the middle of a corner. So I drove normal for a little while and didn't feel anything out of place; no codes showing. So I upped my pace a little and get into a corner and it happened again. This time I noticed that it happened right around the same time that I came into contact with some small wash-board type bumps, nothing major at all, you woudn't even notice them normally. So the car lurches, pulls to one side, and slows itself a tad bit. hmmm.

So I turn off PSM, wick up the pace a bit and go through some corners now trying to hit the small bumps and I can't get it to do anything. So I turn PSM back on and hit a few corners aiming for the bumps and it's fine. Then I go around another corner and it did it again.

No fault codes on the dash display at all. So now I'm a little freaked and I don't trust the car. I know that if I take it into Porsche and it doesn't read any fault codes there probably isn't a whole lot they can do. They're not going to go actually drive it at a good pace through corners to duplicate the problem.

Anyone have an Idea what it may be?

Are you running different brands of tires on front/rear? What you are describing has happened to me since I made the mistake of mixing tire brands. My next pair will depend on whether the front or rear go first. My guess is the rears (RE050's) will go first even tho they are a better wearing tire than the PZero's on the front, which are better traction tires. At that point I'll put on a full set of som'thin.

I'm interested in how your situation resolves. Good luck.

I'm running Michelin Pilot sport Rib's front and back.

[Dus10R]

Went for a drive today up one of our local curvy roads. Car was great up and most the way back; but then I go into a left hand corner and right about the apex I hear a quiet sound that sounds like I just drove over a small cattle guard, the car instantly starts to understeer and pull to the outside of the corner like a brake was being applied, then it stopped and was fine. Luckily I was driving fairly mellow at the time.

It freaked me out a little because I don't want that happening while the pace is upped, in the middle of a corner. So I drove normal for a little while and didn't feel anything out of place; no codes showing. So I upped my pace a little and get into a corner and it happened again. This time I noticed that it happened right around the same time that I came into contact with some small wash-board type bumps, nothing major at all, you woudn't even notice them normally. So the car lurches, pulls to one side, and slows itself a tad bit. hmmm.

So I turn off PSM, wick up the pace a bit and go through some corners now trying to hit the small bumps and I can't get it to do anything. So I turn PSM back on and hit a few corners aiming for the bumps and it's fine. Then I go around another corner and it did it again.

No fault codes on the dash display at all. So now I'm a little freaked and I don't trust the car. I know that if I take it into Porsche and it doesn't read any fault codes there probably isn't a whole lot they can do. They're not going to go actually drive it at a good pace through corners to duplicate the problem.

Anyone have an Idea what it may be?

Are you running different brands of tires on front/rear? What you are describing has happened to me since I made the mistake of mixing tire brands. My next pair will depend on whether the front or rear go first. My guess is the rears (RE050's) will go first even tho they are a better wearing tire than the PZero's on the front, which are better traction tires. At that point I'll put on a full set of som'thin.

I'm interested in how your situation resolves. Good luck.

I'm running Michelin Pilot sport Rib's front and back.

Wow...kind of disheartening. I've been told by others on other forums that this is probably normal. That bites! Not real confidence inspiring to be driving your car through a bumpy corner and the car automatically applies a brake to one wheel which unbalances the car. PASS: Porsche Anti-Stability System. Seems like that would be a very big glitch which could open Porsche up to potential law suits if there happened to be an accident caused by their Stability Management program.

[somahone]

hi,

I have a 2001 996tt with Tiptronic and have spent some time driving less than perfect roads and have found PSM activating in some interesting circumstances:

a) steep downhill winding tight curves, off the throttle, the PSM activates with no foot brake application, throttle application or oversteer/understeer situation. What I believe is that the PSM detects wheel slip on the tight steep corners (steep hairpins) and applies corner braking to 'help' correct the situation. This happens even if you think your speed is ok for the corner but PSM detects some wheel slip, you might just catch the PSM light, but most times your too busy working out what happened, rather than catching the PSM light flash. you might hear the typical sound of ABS, no event is logged.

B) on rough tarmac with sharp dips and bumps and at speed, PSM activates which I believe is again caused by wheel slip detection as a tyre breaches a dip/bump combination, or the rear end steps off (sideways) on a bump. Again you think the speed is fine and probably is but the road surface upsets the road/tyre contact and PSM steps in. Again it's quick you might notice the brake pedal push back if your decide trail braking, and probably missed the PSM light flash. I've had this happen at 180kph mid corner on a sharp short bump.

In all the cases PSM has activated when road speed has been ok for the corners, but the road undulations cause PSM to interpret a wheel slip/traction issue and then activates, which can be take one by surprise and further upset the cars balance. I most cases the PSM intervention is quick and short and leaves little time for the driver to assess what has happened, except after the event.

Scott

[Dus10R]

hi,

I have a 2001 996tt with Tiptronic and have spent some time driving less than perfect roads and have found PSM activating in some interesting circumstances:

a) steep downhill winding tight curves, off the throttle, the PSM activates with no foot brake application, throttle application or oversteer/understeer situation. What I believe is that the PSM detects wheel slip on the tight steep corners (steep hairpins) and applies corner braking to 'help' correct the situation. This happens even if you think your speed is ok for the corner but PSM detects some wheel slip, you might just catch the PSM light, but most times your too busy working out what happened, rather than catching the PSM light flash. you might hear the typical sound of ABS, no event is logged.

B) on rough tarmac with sharp dips and bumps and at speed, PSM activates which I believe is again caused by wheel slip detection as a tyre breaches a dip/bump combination, or the rear end steps off (sideways) on a bump. Again you think the speed is fine and probably is but the road surface upsets the road/tyre contact and PSM steps in. Again it's quick you might notice the brake pedal push back if your decide trail braking, and probably missed the PSM light flash. I've had this happen at 180kph mid corner on a sharp short bump.

In all the cases PSM has activated when road speed has been ok for the corners, but the road undulations cause PSM to interpret a wheel slip/traction issue and then activates, which can be take one by surprise and further upset the cars balance. I most cases the PSM intervention is quick and short and leaves little time for the driver to assess what has happened, except after the event.

Scott

I think you are spot on...

It only happens when going down hill on a fairly steep road, and the PSM light is coming on, I just didn't notice it before. Still doesn't give me any warm and fuzzies... it throws the balance off pretty bad.

[Q-Ship986]

In addition to the tire advice (proper tires, proper inflation), I am wondering, do you need new shocks/struts? --Brian

[Danyol]

Guys,

I'm experiencing the "bump activation" exactly.

I started noticing it only when I replaced my rear tires with a different brand (same spec diameter from each of the suppliers websites). I was also noticing it in curves too (higher G, 50mph) the tendency was reduced when I dropped the front pressure a couple of PSI.

I suspect it's different compound adhesion front and rear. The rears I had previously (P-zeros) would break traction a lot earlier than my new set. I still have a lot of tread left on the P-zero fronts but I may have to toss them anyway.

MH

[Danyol]

Ok guys, after 1k of wear on the the new rears the PSM appears to activate a lot less. I still have the original pzeros on the front and the new tires on the rear...very strange.

[gv95762]

Understanding these cars requires knowledge of vodoo.

Last night I went out for a test drive after installing a new MAF -- things were looking pretty good, car was pulling strong making between .8 and .9 BAR. So for one of my test runs I pulled off to the side of the road to a complete stop, then took off under full acceleration, got up to about 85MPH then backed off the gas, the second I did that the ABS and PSM warning lights went on, and gave the message to bring in to the dealer, and the warining lights would not go off. Got back home pulled the fuse, and disconnected the battery, lights are off, will go for a test drive when the rain stops.

Any ideas as to what may have caused this? I have the same brand tires on front and back, adjusted to recommended PSI by Porsche.

Thank you. :huh:

[wross996TT]

Get the codes....unfortunately those lights tend to indicate MAF issues, but it could be a leak as well. Why did you install a new MAF? Was it installed properly? Was it the right PN?

Any time you disconnect the battery you will get a soft reset of the DME (appears as though codes are erased, but they are not unless the conditions do not exist for multiple starts)...if the conditions that threw codes do not continue then you are good to go, if not then you will get codes again.