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Traction Control Question

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Below is how the Boxster traction control system supposedly works in a 1999, does anyone know if the 996 C2 Traction control system works the same way?

Option P37, Traction Control consists of two separate items, Active Brake Differential (ABD) and Anti Slip Regulation (ASR). When one of the rear wheels begins to lose traction, the ABD applies the brake to that wheel. If both wheels lose traction, the ASR reduces engine power until traction is regained. The Traction Control switch on the dash turns off the ASR, but not the ABD. The ABD is always in effect until you reach 62.5 mph, at which time it automatically deactivates. Because the ABD is always in effect and is applying braking not under your control, control freaks may not wish to order this option.

In particular is ABD always on for the 996? in Autox it seems that it should not matter if you turn Trac on or off as speeds are usually under 65 mph. Has anyone tried disconnecting the system and adding in a Quaife Differential?



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I'll take a stab at this. I believe you can disable the ABD or TC in a 996 at speeds under 65. In Autox it does matter. Even with the pendulum effect of the engine way out back, having TC on will brake the rear wheel(s) and limit the rotation of the rear around a turn. I've seen the ABD described as a system that uses the brakes as an electronic version of a limited slip differential. I've felt it on the street and I've felt it both on and off in Autox at speeds certainly below 65 mph.

I'm unfamiliar with the option code of P37. In my '99 US 996 tip coupe, option code 222 is for "Traction Control". Then there's an option code 224 for "Automatic Limited Slip Differential". I believe the Traction Control is the ABD. Exactly how the two work together I don't know and I'd love to have it explained.

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Additional information from Loren in months past:

The LSD on a MY99 is only 40%. From the tech manual:


To get the engine’s power safely to the road in a standing start, slip is limited to 40 percent. Once under power, the slip factor changes to 60 percent because the engine no longer is operating at its maximum torque and also because this configuration helps minimize oversteer under load changes through a turn.

Also from Loren:

I do not know everything about the early options and TC was only around for the C2 in MY99. Traction Control (TC) is a combination of anti-slip control (ASR) and Automatic Brake Differential (ABD). TC prevents spinning of the drive wheels when moving off and accelerating. It does this through a series of sensors (also used by the ABS system) and controlling individual wheel braking. By doing so driving stability and traction are improved over the entire speed range. PSM includes the functions: ABS, Traction Control (TC), ABD, MSR (engine drag torque control). ABD is part of TC and to my knowledge was not sold separately - together they formed the early version of PSM.

The official name (in the Porsche parts list) for option 224 is "Automatic Limited Slip Differential". There are no parts in the parts list that identify with a M 224 label - so what is it? ABD? maybe?

Technically the option 220 "Locking Differential 40%" is also "automatic" since the multiple-disc limited-slip differential causes locking when one wheel begins to slip. This is the mechanical LSD we all know.

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