PSM Failure

[The Beanster]

During an afternoon session on the track yesterday (at NJMP Lightning) my car started to abruptly brake itself during any hard right hand turns. It was clearly the PSM kicking in but I have no idea why. It went from bad to worse so I pitted in and restarted the car. The issue continued though. I tried disconnecting the battery for a few minutes as well, but no luck.

I ran the short tests with my Durametric cable and it found several issues. It is showing that the PSM valve relay is active and that the FL valve inlet and out are active. The other 3 sides of the car do not show that these valve are active.

After a short while, the dash display read "PSM Failure" and would not let me enable Sport mode. I reset the faults and drove the rest of the day at the track with PSM turned off. I did notice that ABS worked fine during these runs.

Any suggestions for a place to start diagnosing the issue? I dont have much time until the next track event (VIR) but I really dont want to hand the car over to a stealership.

Edited October 21, 2013 by The Beanster

[Loren]

I think it would be helpful if you would give us the fault codes.

All tires are the same size, make and have similar wear?

Likewise with wheels same size and width per axle?

[The Beanster]

Yeah... I figured that but the codes are gone now. I should have written them down but I was so eager to get back on the track that I just cleared them and took off again. This morning, there are no codes after a 30 minute street ride. I guess I need to find an empty parking lot and do some wicked cornering to tease the PSM into activation. I will try that this afternoon and report back.

Some other tidbits...

• Tires are same size with no noticeable difference in wear.
• Wheels are correct sizes.
• Brake lights function as normal.

I read that a bad MAF can cause this but I dont understand what the MAF has to do with PSM. And in my case, the car seems to only cause this issue when turning right.

Edited October 22, 2013 by The Beanster

[Loren]

The control unit in the car constantly talk to each other so the ABS/PSM talks to the DME and get all sorts of information such as engine speed, load, etc. Likewise the wheel speed and brake actuation go back to the DME.

I think your best bet is to re-run the diagnostics using the Durametric and reporting the faults here.

[The Beanster]

I just took the car out and did some wicked circling around an empty parking lot. I think I felt the PSM kick in two or three times. I then stopped and plugged in the Durametric without shutting off the car and there are no faults being shown.

The only fault name that I can remember from this past weekend was one about Sport Mode failure. But the rest have escaped my memory. We're heading to VIR next weekend and I dont want to worry about PSM (yes, I need it on the track). Any thoughts for things to look for and what I might be able to check while at the track if this happens again?

[The Beanster]

I checked the wheel sensors last night with the Durametric tool and found no issues. However, I did find that my front right tire has less rubber than the front left. The area where it is most noticeable is the outside edge (closest to the wheel face). This seems odd to me since it is the "inside" wheel/tire for a track that is largely right hand turns.

It seems surprising that the PSM would kick on with such a small change in available rubber.

The tech at the indie shop I use says it could be that the sways are set too firm. I use GMG bars (firm in rear, medium up front).

Any thoughts?

Edited October 25, 2013 by The Beanster

[binger]

Its very unlikely that your sway bars are the issue. Porsche Cup car teams use much more sway bar then you are. I was called to a shop to diagnose a MZB with a similar issue. The shop had replaced all the wheel sensors, Yaw sensor not resolving the original customer concern. I put a lab scope on each wheel sensor to prove that was not a tone ring or a bad sensor. The waveforms all looked normal now for a test drive. During any hard left hand turns I could hear and feel the system kicking in. Now I am scratching my head back at the shop what is going on I have proved that the wiring, sensors and tone rings are good.

Then I remembered a friend that worked as a tech rep for one of the largest tire distributors in the US. He works with all the factory techs. for support issues. I called him for some insight on my issue with this car. He recommended swapping the front tires with the rear to see if the issue would stop. I told him the tires were wider in the rear then the fronts. He said if they dont rub on the fenders its ok for testing at this point. The shop changed the fronts with the rears tires then we went for a test drive. The issue went away and was solved. What I learned from the tech rep was in there track testing the belts move inside the tires and throw the PSM system for a loop. This can happen on older and or defective tires.

If I were you I would scope all the sensors to make sure you re not just throwing tires at the issue. However it sounds like the car is ready for a new set of fronts anyway. Hope this helps good luck at the track this weekend!

Edited October 26, 2013 by binger

[The Beanster]

Thanks for the info. I had a hard time believing it was the sways.

Can you give me some details to "scope the sensors"?

[binger]

Here is a website that will explain diagnosing ABS systems.

http://www.picoauto.com/tutorials/diagnosing-abs.html