Paul D

Prepping an '04 Boxster for PCA Club Racing this season and need to know if it is possible to disable the PSM, but keep ABS fully functional. I've done some searches here, but couldn't find anything conclusive. Any help would be appreciated!

Rick DeMan

Hey Paul,

Give me a ring..I will give you the scoop on what needs to be done... Not easy and not inexpensive but has to be done to race that car, otherwise the brakes will be really whacky...

jakermc

Isn't it just as easy as unplugging the cable or even just toggle the dash switch to 'psm off'? On my 2003 996 I am able to do this and the ABS brakes work perfectly.

Rick DeMan

Nope.... not at all....

jakermc

So is that because the Boxster was programmed differently than the 996 or because they did something different in 2004 from 2003?

I am 100% certain is works like that on my car so I am just wondering what changed.

mobonic

I know in 997's that they run in Grandam.. you need to replace the ABS module and ECU to a new BOSCH system and its costs about $10K.

The 2005+ cars are very finaky about electrical changes and the car will go into limp mode..

BGB Motorsports in FL or Synergy Racing @ VIR would be great shops to go to that have done this before.

I have heard great things about Rick Deman too... so Im sure you will be in good hands.

GTgears

DeMan Motorsports runs 3 (or is it 4?) Boxsters in ST class in Grand Am.

jakermc

Pretty sure DeMan is not running the stock ABS system. Lots of threads on here about motorsport specific ABS packages versus stock ABS, but the original poster asked if there was a way to disconnect PSM and keep the street ABS fully functional. On my 2003 996, it is. You might not like the street ABS system in a race application but it does in fact work as intended by the factory with the PSM disabled.

I'd like to understand if that is in fact different for a 2004 Boxster, and if so, why?

Rick DeMan

We are running the factory ABS systems in the G/A race cars, they work just fine. BUT, they are the original NON PSM units. The ABS/PSM unit in the 03-04 Boxster does not fully turn off when you hit the PSM button to OFF... it is still integrated and will cause everything from low pedal to applying the rear brakes at extreme slip angles. Simply turning off the switch does not correct this, as a matter of fact, there is no way to eliminate the integration. The only way to get it correct for a true track car with sticky tires and race suspension is to replace the unit with the NON PSM unit from the same year as well as the wheel speed sensors and harness connectors.

jakermc

Interesting, certainly different that what I have experienced. In fact Patrick Long comented that my car's brakes felt as good as any Cup car his has driven. (He was driving it on a track with smooth braking zones, the stock ABS defficiencies pop up when it gets bumpy)

I don't use the switch on the dash, I physically pull the plug leading to the PSM unit at the connection to the PSM unit. PSM is completely disabled and the stock ABS continues to work with no side effects. Running Cup calipers, Cup sized floating Brembos, very stiff suspension, Hoosier slicks, and a mild camber set-up.

Strange that the Boxster and the 996 would work differently.

rlm328

Aren't we comparing apples to oranges in trying to equate a 996 to a 985?

Paul D

Rick -

Thanks for the response! It sounds like this is a non-trivial modification when you say "The only way to get it correct for a true track car with sticky tires and race suspension is to replace the unit with the NON PSM unit from the same year as well as the wheel speed sensors and harness connectors."

I will call you this week to get all the gory details. Talk to you later!

924RACR

Don't be too sure about that. The PSM fully-functional ABS calibration is not likely the same calibration you're getting when faulted out. Furthermore, with all the mods to the car... things get really, well, different...

Motorsport ABS is yet another story entirely

jakermc

Oh, I'm not sure. But Pat seemed pretty convinced. lol

My point is, before spending lots of money modifying the stock system, pull the plug and find out what it feels like. With my set-up its a non issue, the original poster may find the same thing. Would be a good thing to find out before writing a check.

I might also suggest that if the ABS is kicking in, you might be doing something wrong as a driver. If I am on a smooth track and I feel the ABS, I know I screwed up. On a bumpty track it kicks in, goes to black ice mode, etc. but that is a limitation of a stock ABS system on a modded car. Unplugging the PSM did not cause that. I've felt the same thing in non-PSM cars. I could spend lots of money to put in a motorsports ABS system to fix this, but then I remember that this is club racing and there is no prize money.

924RACR

I think you're mistaken in thinking there's a difference between PSM and ABS...