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ABS sensor signal as veh speed sensor.


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Depending on the number of teeth the ABS hub wheel has, it might be too high for most ECUs, only Thunder would have a high enough HZ rating to count that quick. There are converters that will change the frequency from say 1200Hz to under 600Hz that would then be usable in most ECUs. This has been covered a few times in other threads. Mostly using ABS sensors for traction control etc.

Now, looking at the 2004 WRX/STI wiring diagram, it relies on the gearbox speed sensor for at least the stock cluster. So if you don't have one, the speedo won't work as well. I looked to see if the ABS computer has a SPD output (like some Toyota units) but you are out of luck there. My best advise, chase up a sped sensor and install it into your new gearbox.

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Do you have DCCD in the new gearbox + a control unit for it in the car? As @wastegate said there is no 5v pwm output from the ABS computer in this model, neither is there a canbus output like in the newer ones. Your options as I see them are:

1) swap the ABS controller for a newer model with canbus output, or maybe an early 2000's legacy which I think has a speedo out signal wire. You will need to do a lot of research before doing this, and if you have DCCD, it expects to see passthrough of the ABS wheel sensor signals into the DCCD. Finding an abs computer that has DCCD outputs and doesnt require some other canbus input to keep it happy would be possible but quite tricky.

2) install a speed sensor in the gearbox as suggested above. There are a few posts on NASIOC and other forums on how to do this as it was kind of popular a while back to get 6speeds into pre-canbus cars. It requires drilling and tapping holes into the gearbox, and I think it requires a tone ring to be installed onto one of the shafts in the gearbox. Its not a simple tasks and requires removing the gearbox.

3) get one of the frequency reducing boxes out there (various posts on here to build them for <$20 or dakota digital & a few other places sell ready to go models), tee into the ABS->DCCD wiring for 1 or more of the wheel speed sensors, and make sure you leave the original wiring in place so DCCD still works. Run this tee'd signal into the frequnecy reduction box and output into a DI on the ECU. This gives you speed in the ECU. Then configure one of the aux outputs 1-4 as speedo out (set source to the DI you are receiving it on). connect this to the dash input that used to come from the gearbox so your dash has working speedo. (make sure you disconnect the old dash output->ecu input wire at the ecu) 

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