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Tapping into the ABS system to get wheel speed data

Old 04-03-2011, 04:53 PM
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manalex
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Default Tapping into the ABS system to get wheel speed data

I have a 1999 996 C2. The car is equipped with ABS, but no Traction Control. I believe this particular model does not have a CAN bus system. This is a dedicated track car and I'm in the process of selecting and eventually installing a data logging system. To that end I'm investigating the possibility of tapping into the ABS system in order to get the wheel speed data for each of the four wheels. This data, along with various other parameters, will be logged while on the track.

I know this has been done on E36 BMWs but have not been able to find any data with respect to Porsche. I also understand that these units are very sensitive and the last thing I want to do is upset the ABS system. I believe the sensor is a Bosch unit-if that helps. Does anyone have any experience with this mod?

If not, can someone provide the ABS wiring diagram and the specifications for the ABS wheel speed sensor? This would help me continue my research.

Thanks in advance,

Alex
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Old 04-03-2011, 07:25 PM
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Geoffrey
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The ABS units in the Porsches have square wave outputs from the ABS control unit. They range from 2 (both fronts) in the 964, 3 in the 993 (both fronts and a rear), 4 in the 993 turbo / c4s (one is undocumented). I know the 986 / 996 units have outputs too, but I don't have a drawing handy. You'll look for ESO Front Right, ESO Front Left, etc. on the drawing to find the pin number. You can tap into any of these ESO outputs and not affect any other function of the ABS Controller.

I've done this on the GT3 Cup unit which is fundamentally a very similar system to what is in your car.

DO NOT try to tap into the wheel speed sensors direcly. This will create an issue since the common negative of the sensors is a floating ground where the ABS controller references voltage from. If you try to share a floating ground with another device, you will most likely have an issue.

Last edited by Geoffrey; 04-03-2011 at 08:02 PM.
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Old 04-03-2011, 08:21 PM
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manalex
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Excellent, exactly what I was looking for!

I understand this is a wiring diagram for the MY99 996, but I don't think this is the drawing you are referring to:

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But if you find it please let me know. I'll keep looking as well. Also, what does ESO stand for?

Thanks,

Alex

PS-wish I could afford the Motec.
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Old 04-03-2011, 08:27 PM
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Found it...

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Tough to see but it looks like:

ESO FL---->PIN 25
ESO FR---->PIN 26
ESO RL---->PIN 23
ESO RR---->PIN 24
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Old 04-03-2011, 08:43 PM
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amso3
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I have not heard of anone making this work. Not sure the signal is adequate for data systems to use. Geoffrey, what do you think? It would be fairly easy to install magnetic wheel speed sensors, but if you are looking at AIM and GPS you don't need any of that. The only value I've seen using 4 wheel speed sensors is to check for wheel lockup (997 Cup cars) which should not be an issue with ABS cars.
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Old 04-03-2011, 09:22 PM
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Geoffrey
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Yep, those are the signals you need. Set your logger to read a digital square wave signal and you're all set. I cannot remember if they are +5v or +12v signals since it has been many, many years since I figured this all out. I would guess ESO stands for Electronic Speed Output, but then again, it may be a German acronym. It is this set of outputs that drive the speedometers, tiptronic, onboard display computer, etc. There are some pins that are assigned ESO outputs that are not even on the wiring diagrams. For instance, the 4 channel 993 ABS controller found on the turbo and C4S has only 3 listed on the diagrams. I used an oscilloscope to find the fourth.

The signals are perfectly adequate for data logging functions. I have used the ESO outputs with MoTeC on 964, 993, 996 Cup cars, BMWs where I've installed the GT3 Cup ABS system, and 4 channel 996 ABS systems retrofitted to an older car and BMWs.

In my personal car, the ESO outputs from the 993 GT2 Racing ABS Controler feed my MoTeC ADL/2 logger which then uses CAN to send them over to the ECU for traction control and pit speed limiter functions.

but if you are looking at AIM and GPS you don't need any of that. The only value I've seen using 4 wheel speed sensors is to check for wheel lockup (997 Cup cars) which should not be an issue with ABS cars.
With all 4 speeds being logged, you can see a) when a wheel comes off the ground, b) when the ABS system is pulsing a wheel, c) differential lockup, d) wheel slip under acceleration and e) wheel lockup when you turn the ABS system off, just to name a few uses. This is one of the reasons I much prefer a beacon based data logging setup to GPS. With an advanced Logger and software analysis such as MoTeC, you can do enhanced math functions to help with much of this analysis.

If you own an oscilloscope (and any good data guy has one), you can see the signal for yourself.

Last edited by Geoffrey; 04-04-2011 at 10:26 AM.
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Old 04-03-2011, 11:19 PM
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Thanks for your help Geoffrey and sharing your experience with us. I'll make sure to post the results of the install once completed.
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Old 03-17-2014, 06:58 PM
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I know this is an old post, but wondering how this went?
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