Difference between Traction Control sub-systems?

What's the functional difference between locking differential and active brake differential in reference to Traction Control on a 996? Thanks.

Locking diff'l is a mechanical system that prevents the diff'l spider gears (or equivalent) from free-wheeling, and thereby forces engine torque to the wheel with traction. "Brake" diff'ls use the Anti-lock braking system to moderately apply the brakes on the non-tractive, free spinning, wheel, thereby forcing engine torque to the wheel with traction. Assuming ABS already, no additional mechanicals to wear out, slightly less life for the brake pads. "Functional" difference is minimal, ABS LSD is possibly quicker reacting.

I'm confused. Does my '02 C4 have both?

No. 996's have ABD (Automatic Brake Differential) J

The locking diff was an option called Traction Control and I believe was only available on 1999 model C2's. I know I had it on mine. Karl

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Mark Wheeler: <strong>What's the functional difference between locking differential and active brake differential in reference to Traction Control on a 996?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">As Karl stated, LSD (LIMITED-SLIP DIFFERENTIAL) was only available on the '99 C2 models. Here are the differences in Porsche's words: " ABD (Automatic Brake Differential) A type of traction assistance which applies the brakes to a slipping wheel, transferring torque to the opposite wheel. ABD systems generally operate at lower vehicle speeds. LSD (Limited-Slip Differential) A type of differential which limits the degree of variation in wheel speed between the two driven wheels, thus reducing wheelspin under conditions of poor traction. The limited-slip differential begins to restrict the torque supplied to a spinning wheel by a predetermined amount, reducing the speed of rotation of the spinning wheel to that of the wheel which still has sufficient grip. The result: traction is not interrupted appreciably, allowing the car to keep moving." With the advent of PSM, LSD is no longer compatible on the Carrera and Carrera 4 but ABD is now part of PSM.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by aktundramonkey: <strong>I'm confused. Does my '02 C4 have both?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Your Carrera 4 has PSM. Here's Porsche's description of it: Porsche Stability Management System (PSM): The 911 Turbo and Carrera C4 all-wheel drive models are equipped with a significant handling innovation designed to stabilize the car when driver loss of control is impending. It�s called Porsche Stability Management (PSM). The system is optional on both Boxster models and the two-wheel drive Carrera. PSM incorporates the components of the previously used Boxster and Carrera 2 Traction Control system � Automatic Braking Differential (ABD) and Anti-Slip Regulation (ASR) with additional sensors. But a new and innovative element of PSM is also present: a high-tech control unit that responds to help the driver maintain control when the vehicle oversteers or understeers. Here�s how this system works: A number of sensors provide input to the master control "brain." These include the four ABS wheel-speed sensors, plus a yaw-velocity sensor which detects movement around the car�s vertical axis, a transversal-acceleration sensor which responds to sideways movement of the vehicle, and a steering-angle sensor which detects the direction and speed of the steering wheel input from the driver. The master control unit continuously checks and compares input from the sensors to determine the vehicle�s direction and movement and how it differs from the direction chosen by the driver based on steering-wheel input. If the system senses that the vehicle is deviating from its proper path while accelerating or coasting � by oversteering or understeering � it reacts with the following corrective action: If oversteer is sensed, the brake at the front wheel on the outside of the bend is activated If understeer is sensed, the brake at the rear wheel on the inside of the bend is activated If selective brake applications are unable to stabilize the car, the engine management system reduces or increases torque by varying the ignition timing or by varying the throttle opening In cars equipped with Tiptronic S, the automatic shift process is controlled in order to ensure that changes in torque do not cause the car to be unstable Hence, the Porsche Stability Management system has components that help to maintain control during braking, as well as components that help maintain control during acceleration, cornering, and coasting. While PSM significantly increases the stability at the limits of adhesion, it cannot overcome the laws of physics, and must not be thought of as an antidote to irresponsible driving. Porsche Stability Management provides numerous benefits to the Porsche driver: Promotes optimum traction and steering accuracy when accelerating, even on surfaces with varying adhesion levels Helps compensate for load-reversal reactions when coasting, or during partial braking applications Helps avoid oversteer, such as might occur during rapid steering movements Reduces understeer when turning sharply into a bend � especially on compromised road surfaces Promotes shorter braking distances and improves stability when brakes are applied, especially when cornering on surfaces of varying grip Maintains high level of sportscar handling and driving safety by maintaining outstanding agility Allows driver to switch PSM system off in order to adopt a deliberately more-active driving style

Great post, Viken! A somewhat related question: I assume that the algorithm in a C2 is different than a C4 - the front wheels now also drive, so it's not just about braking. Is the algorithm for a C4 or C4S different than a Turbo?

Great info gents! Thank you. Mark

C4... Since the front wheels rarely have high engine torque applied it's unlikely that PSM would need to apply "trac" (moderately brake a front slipping wheel) and to do so could "upset" ("radical" torque steer) the steering, like having a front LSD, not very common even for most SUVs. I would guess dethrottling would be the first effort the algorithm would use with front wheel slippage.

Very great post. Basically if you have traction control you typically have an open or peg leg, non limited slip differentail that applies brake to the wheel slipping typically the right rear- hence peg let. with the psm it brakes the wheel spipping at that corner. MB calls it esp. It uses wheels sensors and in some circumstances yaw sensors- come car to monitor the force, then applies the brake. Personally I hate it. It is typically very invasive, however Porsche is the best at doing it and is managable but I would still turn it off if I had the option. I opted to get a 99 because of the fact that is has nada! I do however have traction control, which means I dont' have a limited slip, which is really lame but at least I can do what I want where I want. A small footnote however, with the average driver these control systems time and time again are a life saver for someone going in over their head. For someone more experienced or otherwise they are invasive and try to do the work that you should be doing with by limiting a nice slip angle or a power oversteer slide etc. Porsche is definitely the best of the bunch for sure though concerning these systems.

What are the functional differences between PSM and wider tires thereby more contact patch and traction?

psm just uses wheel sensors to modulate the braking and possibly yaw sensors or something like it but don't know, Wider tires and more traction would just make it not kick in as soon. Also with larger rims it would make it looks slower. Basically it seems to me that it looks at all the wheels and if one is going x amount% faster then it brakes it as it is loosing traction. I don't know that much about the inner workings but the theory typically is the same amongst systems. I do seem to remember that the psm uses the same sensors that the litronics use for adjusting height which are mounted front to back on the track arm or something? but I could definitely be wrong. I bet loren would know more. I don't have psm, although I do have traction control and it does get in the way as i have a c2 and like to get maximum slip angle which like to kick the traction control on here and there and upset the balance a bit, so I turn it off rutinely. Around town however I could care less it seldom comes on like a good system- read PORSCHE does.

I searched this set and the 06-23-2002 postings for 'traction control' systems but need to clear up the limited slip differential issue for the 996. (I might buy a 996 for street and track) On the 1999 USA Spec 996 two wheel drive, manual transmission model... It is a fact that there was an option of ' traction control' officially called Automatic Brake Differential (ABD). Was there a traditional 'limited slip differential' for this car? If so was it standard or an option? I think SPR and some others are saying there wasn't any factory rear LSD for the normal US Spec street 996, ever. If that is true my choices within the 996 C2 fleet are; no special traction system, ABD, and PSM (starting MY 2000)?

no just that I don't believe that you can have traction control with a limited slip diff. That is how my c43 was as it had to be open to work with the brakes etc. I am pretty sure though that they did offer limited slip in 99 just not with traction control as they should be mutually exclusive-

Thanks for the quick reply. I understand what you are saying about 'mutual exclusive' with LSD and ABD. I don't have the factory literature for the 1999 so I would like to get the facts so I can pick the appropriate car for my desired use.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by 993_996_enthusiast: <strong>I searched this set and the 06-23-2002 postings for 'traction control' systems but need to clear up the limited slip differential issue for the 996. (I might buy a 996 for street and track) On the 1999 USA Spec 996 two wheel drive, manual transmission model... It is a fact that there was an option of ' traction control' officially called Automatic Brake Differential (ABD). Was there a traditional 'limited slip differential' for this car? If so was it standard or an option? I think SPR and some others are saying there wasn't any factory rear LSD for the normal US Spec street 996, ever. If that is true my choices within the 996 C2 fleet are; no special traction system, ABD, and PSM (starting MY 2000)?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Traction control (not ABD) was an option on the 1999 C2, I had it on my car. It included a LSD as part of the package. 1999 was the only year this was offered and IMHO it is the hot set-up for the track. Karl

I have a 1999 with both Traction Control and the limited slip differential. I can't remember the option codes, but they are posted under the trunk lid on a paper sticker. It is a nice feature off the track too (especially in the snow).

Really? interesting mercedes is different I guess. I wonder if I have the limited slip since I have traction control also. I will have to run the options. Yeah if someone could post what that code was that would be great!

Option code was 476. As I said earlier, if you have traction control on a 1999 996, you also have LSD. LSD came automatically and only if you ordered the traction control option. Karl

My '99 996 has both ABD (224) and Locking Differential (220) option codes on the options sticker.

an man now I am going to have to go down to the car and jot down all my options to see which I have! brb

I also have 220 and 224. locking differential and active brake diff.

btw I have traction control also and it didn't list the limited slip code

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Karl S: <strong>Option code was 476. As I said earlier, if you have traction control on a 1999 996, you also have LSD. LSD came automatically and only if you ordered the traction control option. Karl</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Karl is absolutely correct. I have the traction control/LSD option on my car. The electronic traction control is defeatable by a dash mounted switch. It must be turned off (if that's what you want) each time you start the car, but stays off as long as the engine is running. For the street it's usually not intrusive but at the track I always turn it off as it has a tendancy to shut down engine power in low traction situations. With the electronic system off, the mechanical LSD is able to provide maximum possible traction at the rear without interupting power delivery.

Interesting I have the traction control but it doesn't say limited slip as I noted above just locking diff and active brake diff. or whatever. I guess locking diff is the same as limited slip in terms of the friction on the cones inside but has the electronic coupling like some air diffs for off roading to play with the traction control stuff electronics?

On the 1999 996 the Traction Control (TC) system is based on two features 1) The Automatic Brake Differential (ABD); 2) Anti-slip control system (ASR) ie torque reduction through DME engine intervention if both rear wheels begin to spin. The ABD is only active to 62.5 mph, above 62.5 mph the ABD does not intervene. The ASR is active at any speed unless the TC is switched off manually. Ref. PNA 499 921 Info from the Porsche dealer... Option Code M222 = Traction Control System Option Code M224 = automatic limited slip differential

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by StephenB: <strong>On the 1999 996 the Traction Control (TC) system is based on two features 1) The Automatic Brake Differential (ABD); 2) Anti-slip control system (ASR) ie torque reduction through DME engine intervention if both rear wheels begin to spin. The ABD is only active to 62.5 mph, above 62.5 mph the ABD does not intervene. The ASR is active at any speed unless the TC is switched off manually. Ref. PNA 499 921 Info from the Porsche dealer... Option Code M222 = Traction Control System Option Code M224 = automatic limited slip differential</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">The mechanical LSD was also part of this package. The 1999 order guide dated November 18, 1998 (the time frame when I ordered my car)lists option code P72- Traction Control with ABD and Limited Slip Differential- for $1215.

Thanks folks for your interest and support. Looks like another Porsche AG option code puzzzzzle. So... from all of your comments here is my summary. The USA spec 1999 Porsche 996 two wheel drive coupe with the "Traction Control" option has; locking differential, ABD, and ASR. The option code(s) supporting this vary depending on when the MY 1999 car was built. ABD/ASR systems are a package; ABD uses brakes, ASR uses the engine computer (DME) I think Porsche uses the term "locking differential xx%" and we USA folks use "limited slip differential" but they are the same darn mechanical thing. There is no evidence that one could buy just the locking differential from the order guide for this USA spec car. It appears to me that they stopped using the 220, 224 option codes later in the 1999 production period and went with the P72 (Mike in LA). I am considering buying a 1999 which the salesman claims has traction control. He sent me the option codes and P72 is listed. 476 is used for PSM in model year 2001, and I have seen it mapped to "traction control" but without a model year specified. The only 996 year with traction control is 1999? cause 2000 and newer went to the PSM system. From this set of postings the following have the "traction control" (with on/off switch) on their 1999 996 C2 but option codes vary. Mark Wheeler 220 yes 222 no 224 yes 476 no P72 no Karl S SPR 220 yes 222 no 224 yes 476 no P72 no Mike in CA car I am ??? 220 no 222 no 224 no 476 no P72 yes What do you think?

Mark Wheeler: 220 yes, 222 yes, 224 yes, 476 no, P72 no. Also, I do have the "TC" on/off switch. Thanks for the summary. Mark

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by 993_996_enthusiast: <strong>Thanks folks for your interest and support. Looks like another Porsche AG option code puzzzzzle. So... from all of your comments here is my summary. It appears to me that they stopped using the 220, 224 option codes later in the 1999 production period and went with the P72 (Mike in CA). I am considering buying a 1999 which the salesman claims has traction control. He sent me the option codes and P72 is listed. Mark Wheeler 220 yes 222 no 224 yes 476 no P72 no Karl S SPR 220 yes 222 no 224 yes 476 no P72 no Mike in CA car I am ??? 220 no 222 no 224 no 476 no P72 yes What do you think?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Mark, I didn't mean to confuse the issue, and hope this will straighten out my response, at least. The P72 code appeared in the order guide for the "Traction Control with ABD and Limited Slip" package, however on my underhood sticker I also have the 220, 222, and 224 option codes. The P72 must be an ordering code for the package, while the other numbers are the actual production codes for each individual feature.

Great thread on confirming that the 1999 996 is the only model year 996 with a locking (limited slip) differential--which apparently uses Anti-Slip Regulation and Automatic Braking Differentiation as a package dubbed "Traction Control"--order code P72.