Tapping into the ABS system to get wheel speed

[manalex]

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 investigations.

Thanks in advance,

Alex

[Loren]

Wow member since 2006 and this is your first post!

You are correct the MY99 cars only used CAN for Tiptronic communication.

You will need to pull each wheel speed from the ABS controller (left front trunk location).

Here are the wire colors and connections.

[manalex]

That was fast! And exactly what I was looking for. Have you heard of any one doing this? Also, do you know what type of sensors these are and what the voltage ranges are? I understand that they operate in the sub 0.5v range. I want to avoid tapping into the wiring and inadvertantly changing what is being communicated to the ABS unit itself.

Thanks again,

Alex

[Loren]

I don't know anyone that has done this - usually they just get speed and tach from the OBD II port for the dataloggers.

[manalex]

Loren, I just recieved this post in another forum (rennlist). It appears to come from a gentlemen in NY that is a Motec specialist.

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.

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.

Do you have the drawings he is refering to? Also, can you add anything else to what he is saying?

Thank you again,

Alex

[Loren]

Yes, different outputs on the same controller (see below).

[manalex]

U da man!

I'll make sure to post how it all goes.

Thanks!

[manalex]

Loren:

I'm getting some conflicting info and was wondering if you could help. There is someone chiming in that says the ABS output for the rear wheels is something other than a square wave. Fronts are okay, but the rears will require a bit more research so I can confirm. Do you have any information on this subject that you can bring up? I'm not sure why the rear wheels would have a different output, but I just need to confirm. Also, if you come across the voltage output and confirm it (suppose to be 5v or 12v) that would be great.

Thanks again,

Alex

[Loren]

I think you may need to look at the outputs with a scope as Porsche documentation does not go into controller detail (proprietary info I suspect).

[Orient Express]

Another solution might be to get the speed data from the speedometer signal wire in the cabin. That is the pink/white wire in the relay support bracket. This signal wire provides speed info for things like the PSE, soft top retraction system, and other things. This wire is a universal tap for anything that needs vehicle speed info to work.

[manalex]

Loren:

Can you tell me if there is a sensor that tells you the amount of brake pedal travel? If so, where is it located and do you have the wiring diagram for it?

Thanks again,

Alex

[Loren]

Loren:

Can you tell me if there is a sensor that tells you the amount of brake pedal travel? If so, where is it located and do you have the wiring diagram for it?

Thanks again,

Alex

Sorry, no there is not.