Hi,

I bought a 2011 997.2 c2s this week. It seems to have a problem with the PSM/ABS. If I apply light brakes in a turn it feels like the ABS is engaging. I get that shuddering feeling through the pedal. This is with brake pressure much lighter than required to lock the wheels. On a couple of occasions with a bit more brake pressure it feels like the ABS is kicking in and adding more brake pressure. It has scared me on at least two occasions where I got much more braking in the middle of a corner than I was expecting. If I turn off PSM this goes away. It does have mismatched tires front to back. I'm going to change them next week in case that is messing with the PSM. Any other ideas? Has anyone else seen the same problem?

David

 

My first thought while reading was tire issues. You confirmed a tire problem at the end of your post. So start there as you plan to do anyway and be sure to report back your findings.

 

Are there any faults stored in the PSM system that you know of? What brands of tires, etc? Stock brakes?
Mismatched tires won't necessarily cause issues with ABS/PSM. Unless one of the sets is either completely worn, not load rated for the weight in the rear of the car, or are just a crap/cheap tire with a lot less grip than the other pair, ie the car is seeing dramatically different wheel speeds while slowing and turning.

With the new tires, be sure to get a full alignment, including recalibration of the steering angle sensor. If this is misreading it's correct orientation (as in the wheel is straight, but the sensor reads 20-30 degrees off center), then the car will think you are braking suddenly while loaded in a corner and react to what it feels are incorrect inputs while trying to help save you.

Simon

 

Thanks for the feedback.

Some more info. No faults in the PSM when I got it inspected last week. Stock brakes and suspension. Dealer serviced. The fronts are almost worn out Michelin Pilot Sports and the rears are Toyo Proxes 4 plus and are pretty new. All are getting replaced with Michelin Pilot Sport 4s next week. It does not have any problems when braking in a straight line. Generally in corners if you load the brakes before turn in then it's fine but if you give them just a small input after turn in it happens.

I'll get the wheel alignment. Thanks for the suggestion about the steering angle sensor. In general the car does not feel very stable, even just driving on the highway. It's not bad but less stable than my other car (mercedes gla45). It follows cambers a lot and generally requires attention to keep it going straight. It does pull to the left a bit so definitely needs the alignment. It has 3 weeks of CPO warranty left on it so need to get all problems sorted out ASAP.

The service history says "client states that the brake pedal is slapping the bottom of his foot after releasing the brake". Dealer said "unable to verify". I know what he meant, it's like the ABS is holding the pedal down a bit then releases it and it pops up.

I'll get the tires, alignment and steering angle sensor done this week and let you know how it goes. I'm currently driving it with the PSM turned off because it feels safer but turning off stability control on the road to be more safe is not a good situation.

 

I wouldn't be at all surprised if the stability issues, and maybe even the PSM concern, are directly caused by the Toyo All Seasons mounted on the rear. See it all the time with cheaper tires whose sidewall design flexes excessively when loaded on the rear of a 911, nevermind with the high treadwear rating of that Toyo.
As the car loads in the corner, the yaw rate sensor and wheel speed inputs are probably dramatically different as the rear tire sidewall collapses, which in turn creates a higher wheel speed reading due to a lower rolling diameter (like having a smaller wheel and tire on that corner).
One way to test the theory would be to up the pressures in the rear to see if it makes a difference. Or just replace the tires as planned and work from there. Good luck!

 

Driving on mismatched tires, what do you expect? Different sidewall flex and traction levels all seen by the system sensors. Its a wonder you did not crash.

 

I took it to an independent Porsche mechanic. He drove it and confirmed there is a problem. Replaced all four tires with Michelin Pilot Sport 4s and had a wheel alignment. Now it's less obvious but still isn't right. He tested all the wheel sensors and said they are OK and suspects the ABS control module. That's a seriously expensive part. So it's off to the dealer after Christmas. Hopefully I can get them to reproduce the problem on a test drive. You need to push the car to notice it and it's hard to do unless you are on the right roads.

 

Warped rotors?

 

I hate when people post questions and then never follow up with the actual resolution so he is my delayed reply to my original post. Changing the tires was the solution. I think it was just a bit of paranoia in my second post where I thought the problem was still there after I put new tires on it. Those mismatched tires made it dangerous.

Just sold the car today. Overall it was a great ownership experience over 2 years and 11,000 miles.

 

Thanks for following up on the problem. I had the same issue, after new brakes, tires, ABS module, YAW sensors, wheel speed sensors and a lot of other work, including the regional field tech coming in multiple times, a solution was never found. Link to my thread below.

https://rennlist.com/forums/997-foru...ent-issue.html