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Thread: Vehicle speed output for ABS manual trans

  1. #1
    Registered Member Anzi's Avatar

    2002 Protegé5 manual

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    Vehicle speed output for ABS manual trans

    So I was looking through the service manual tonight, and it seems that the speed signal is interpreted by the ABS computer and sent to the gauge cluster directly, as opposed to being run through the PCM, so long as the car is manual trans. If this is correct, that would imply that swapping an MP3 or MSP ECU into the car wouldn’t affect the speedometer readings whatsoever. Am I right about all this, or am I misreading the manual?

  2. #2
    Registered Member

    protege5

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    That is true for most cars. The ABS ECU interprets the speed signals, (usually through the wheel speed sensors) and outputs to the cluster. The cluster then outputs to the engine ECU and/or cruise control ECU. The engine ECU in a manual transmission doesn't really do much with the speed signal, it monitors it, but really doesn't care how fast you're going, it just cares about fuel trims, o2 readings, air input, etc. so that the motor runs correctly.

    If you don't have ABS however, I believe the signal comes straight from the speed sensor in the trans to the cluster, engine ECU, and cruise control ECU but that's just a guess. Don't feel like looking through diagrams at the moment lol. I believe there's another member here that lives for that kind of action

  3. #3
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    This diagram shows the different speed sensor inputs.
    The black triangle shows the direction of input.
    So it looks like the signal is coming From the ECU To the cluster or From the ABS head unit to the cluster or from the vehicle speed sensor (turbine in the transmission)



    The only time I've heard of the speed sensor being a problem, was when a manual transmission was swapped from an ABS car into a car without ABS.

    Non-ABS manual transmission cars have a turbine in the transmission to output speed data and you have to open up the transmission to install that gear to use it on the car.

    I'm 95% sure you can swap in either ECU that you're interested in and you will not have a problem.

    I don't recall anyone posting about speed data problems with an ECU swap.
    I assume that the other ECU's are equipped to deal with different speed data as well as ours.

    There has been a lot of people who have swapped ECU's and didn't mention any problems.
    Last edited by pcb; 04-04-2019 at 11:11 AM.
    The Diagram Dude

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