PSM?

[Lyn]

My 997.1 C2 has PSM with an on/off switch on the center stack and I've always been curious of what features PSM brings to the table? What doesn't work when you switch it off?

[Mijostyn]

Hi Lyn,

If you are an untrained driver and you drive like I do you best keep the PSM (Porsche speak for traction control) on. It will save your a-- if you screw up. It might also interfere with your fun if you are trained and know what you are doing. Most of us unfortunately, are not trained and we do reflexive things like hitting the brakes in a skid then over correcting and hook spinning the car, a very expensive mistake.

IMHO all 911 drivers should go to a driving school like Skip Barber and learn to handle a car under extreme conditions. Then take your 911 to a large open space or a track where you have plenty of run out and learn what your car AND TIRES do. If you change tire brands or type your car's handling will change. About once a year when my tires are down to 3/32" I go to this huge parking lot at dawn on a Sunday and play Ayrton Senna. They run autocross at this lot and the track markings are refreshed yearly. Some guys like to track their cars but you either have to belong to a group like PCA or spend a lot of money. The parking lot is free and I can go there any Sunday I like. It is a blast after it snows.

Go to your favorite driving spot after you get yourself trained and turn the PCM off and see what happens. It is most definitely harder to spin the car with the PCM on but it is also harder to get the back end around smoothly which is what 911s are great at. Great way to ruin a set of tires which is why I wait until they are almost worn out.

On public roads I always keep the PSM on. Even though you may know every rut and pot hole on a road, road conditions can change dramatically and unexpectedly. An oil spill, wet leaves in the fall, or just a light rain. The price of a mistake on public roads is too high and the PSM is great insurance particularly if your reflexes are getting old like mine.

[JFP in PA]

My 997.1 C2 has PSM with an on/off switch on the center stack and I've always been curious of what features PSM brings to the table? What doesn't work when you switch it off?

Actually, rather than "traction control", PSM functions as "yaw control" to limit the car's ability to get completely out of shape and end up in the top of a tree somewhere. The system uses a variety of sensors (individual wheel speed, steering angle, actual angular momentum of the vehicle, etc.) to try and help keep the car going in the direction the driver intends it to. From the OEM literature:

PSM, which comes as standard, is an automatic control system that stabilises the vehicle at the limits of dynamic driving performance. Sensors continuously monitor driving direction, speed, yaw velocity and lateral acceleration. Using this information, PSM computes the actual direction of motion. If this direction deviates from the desired course, PSM initiates braking interventions targeted at individual wheels in order to stabilise the vehicle.

Under acceleration on wet or low-grip road surfaces, PSM improves traction using the ABD (automatic brake differential) and ASR (anti-slip regulation) functions, giving an agile response. When ‘Sport’ mode is selected on the optional Sport Chrono Packages, the PSM intervention threshold is raised to enable greater driver involvement – particularly at speeds of up to approximately 70 km/h (45 mph). The integrated ABS can further reduce the braking distance. For an even sportier drive, PSM can be deactivated. However, it is automatically reactivated for your safety if either of the front wheels (in ‘Sport’ mode, both of the front wheels) requires ABS assistance. ABD remains permanently active. PSM has been enhanced and now includes two additional functions: precharging of the brake system, and brake assist. If you suddenly release the accelerator pedal, PSM automatically readies the braking system. With the braking system having been precharged, the brake pads are already in light contact with the brake discs. Maximum braking power is therefore achieved much sooner. When sudden braking is detected, the brake assist function applies maximum brake pressure to all four wheels.

So it is a lot more than just traction control.

[Mijostyn]

I stand corrected. Actually JFP, whenever a tire loses its grip on the pavement in whatever direction that would be a loss of traction. Yes, it does a lot more than just modulate the brakes. Whatever, it works great!

Edited November 22, 2013 by Mijostyn

[JFP in PA]

I stand corrected. Actually JFP, whenever a tire loses its grip on the pavement in whatever direction that would be a loss of traction. Yes, it does a lot more than just modulate the brakes. Whatever, it works great!

The yaw control function, its most common activity, does not typically involve any loss of grip or a slide to trigger an intervention and get the vehicle back on track, it is the difference between the car's actual changing yaw angle and the one that should be produced by the current steering inputs, hence its "stability management" title rather than traction control.

[996noob]

Does anyone know where the yaw sensor is located on a 997-1?

[nkjell]

I'll add my $0.02 ... join your local PCA (Porsche Club of America) region and participate in autocross. You'll learn more about your car than you can imagine, in a very safe manner and with professional instruction. And its very inexpensive - in the SF Bay area we pay between $35 and $40 for a day of autocross with an instructor.

...

IMHO all 911 drivers should go to a driving school like Skip Barber and learn to handle a car under extreme conditions. Then take your 911 to a large open space or a track where you have plenty of run out and learn what your car AND TIRES do. If you change tire brands or type your car's handling will change. About once a year when my tires are down to 3/32" I go to this huge parking lot at dawn on a Sunday and play Ayrton Senna. They run autocross at this lot and the track markings are refreshed yearly. Some guys like to track their cars but you either have to belong to a group like PCA or spend a lot of money. The parking lot is free and I can go there any Sunday I like. It is a blast after it snows.

[racerken]

Does anyone know where the yaw sensor is located on a 997-1?

It is located under the passenger seat.  It's a small box with a vertical cylinder.  The lateral sensor is mounted on the center console.  It looks like a pvc valve.  Like JFP said, it's a system of other sub-systems so good luck in messing with it.   :eek:

[Phil_D]

 

I'll add my $0.02 ... join your local PCA (Porsche Club of America) region and participate in autocross.  You'll learn more about your car than you can imagine, in a very safe manner and with professional instruction.  

X2 In just a few autocross sessions I learned so much about the limits of the car, and unlike on the track, when you find the limits it usually results in nothing more than a spin out.  

For autocross I turn PSM off.  On the street I leave it on, but I can say for certain that if you push it hard PSM will not stop the vehicle getting out of shape.