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After 2.5 years in the shop, my car is finally ready to be released....but, there is always a but, the speedometer isn't working. We went through all the normal tests but it is looking like it is the ABS controller. I looked through the archives and the 964 C4 ABS controller hasn't been discussed in a while. I know there was some old commentary about rebuilding the ABS pump with MB parts (not on topic, but maybe in the future) or installing a new abs system (sounds expensive for a street car). I can buy a new one for $4k (not happening) or a used one from Autobahn for $1.5k. Does anyone have any other solutions? Or other things I should look into before biting the bullet? All help appreciated!! Because I know you are going to ask:
There is a signal converter that takes the abs speed sensor signal and converts it for the Speedo. Start by checking that its in place and that there is a signal from the abs sensor.
shoot you have a c4, I have a c2 test harness... would be happy to do for you given you're local but the units are different
a few questions:
ABS is not functional? have you tested the pump and locks function? These can be triggered manually with jumping various wires at the ABS controller (if you want the factory manual and diagrams I can email them to you, pm me).
And, the speedo is not functional, and you've verified the reason why is the signal from the ABS controller? Did you verify the signal with an osciloscope?
Keep in mind, the signal is fed from wheel speed sensor, then converted by a 'relay' looking device then to the speedo.
Here's a good diagram: https://forums.pelicanparts.com/pors...bs-sensor.html
Does anything with the C4 diff, abs, lateral, etc work for you?
I am not getting any, but haven't really driven the car. The pump is working. I think I found an ABS controller that I can "test" to see if that is the fix. I believe we (well maybe my mechanic) has tried everything else, so now we are just trying to eliminate things. The cost of the ABS controller made it last!
01-20-2022, 06:12 PM
ABS Controller
