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Vehicle speed sensor / wiring

Posted by gIGoN, Sep 13, 2019

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  1. gIGoN

    gIGoN Probationary Member

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    Hi guys,

    I'm trying to figure out where is my speed sensor. I have a CE9a EVO III. The speedometer cluster gets the reading via a cable which goes to the gearbox. So i'm wondering the vehicle speed sensor which goes to the ECU is reading the speed from which sensor as the speedo is only a cable which screws on the gearbox.

    I noticed theres a 2 pic socket which goes to the calipers. Are those somehow related to the vehicle speed sensor wiring to the ECU or just solely for ABS? Where does the vehicle speed sensor wiring to the ECU gets the reading from? I'm trying to get it working so I can cutoff certain parameters (eg: launch control) in my Link ECU.
     
  2. steve

    steve DSM Wiseman

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    Can't say for sure how the EVO III is but on a 1G DSM the speed sensor is in the Gauge Cluster and driven by the Speedometer cable from the gears in the transmission.

    The sensor is a reed switch connected to ground and there is a rotating magnet that opens and closes the switch. The ECU counts the pulses in a fixed time period and calculates the speed. It's not very accurate. IIRC the ECU provides the bias voltage to the switch so it can generate the pulses.

    The ABS is a different system.
     

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  3. gIGoN

    gIGoN Probationary Member

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    Thanks for the reply. Which wire exactly is it from the meter cluster?
     
  4. gIGoN

    gIGoN Probationary Member

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    I traced the wire from the ecu and it goes to this socket. Where does this connects to?

     
  5. gIGoN

    gIGoN Probationary Member

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    T
    Traced it again and this socket goes to the column shaft socket (the black thingy which has the wiper amd light arms near the steering. Noticed theres some board inside it connects to. I’m lost after that. Where does it get the reading from
     
  6. gIGoN

    gIGoN Probationary Member

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    I did a continuity test and there id a connection from the socket up to the ecu. I am still clueless where ot gets the speed reading from. Hope someone could shed some lights on this.
     
  7. DSMPT

    DSMPT Proven Member

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    IIRC, EVO 3 ECU is getting pulses from the cluster. That's like 1G DSM like @steve mentioned above. The ABS speed sensors don't affect the VSS signal for ECU.
    There should be a yellow/white wire between the cluster connector and ECU pin #66, that's the VSS signal wire to the ECU.
     

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  8. gIGoN

    gIGoN Probationary Member

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    Thanks for the reply. when u say cluster, means that it's from the back of the speedometer? the one with the blue and brown socket? can i pull a new wire and connect it directly to the ecu?

    There's actually a few green and yellow. Do you happen to know which one (location) is it from the cluster socket?
     
    Last edited: Sep 17, 2019
  9. gIGoN

    gIGoN Probationary Member

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    this is my cluster socket

     
  10. gIGoN

    gIGoN Probationary Member

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    just an update guys, the speedo is actually the centre pin on the blue socket. i did a continuity test and the cable is connected up until the ecu. I'm still not sure why theres still no reading at the ecu.

    i've tried using a different cluster meter and its still not getting any reading to the ecu. :(
     
  11. DSMPT

    DSMPT Proven Member

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    Yes that should be the one.

    How did you test that?
     

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  12. gIGoN

    gIGoN Probationary Member

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    using a multimeter, so the wire from the ecu is ok up until the cluster's blue socket. I tried swapping the cluster meter and there's still no reading as i believe it should be generated by the dash cluster meter.
     
  13. steve

    steve DSM Wiseman

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    Is there any voltage on the wire? I don't have my references with me here in the mountains but I think the ECU provides the pull-up voltage that the cluster reed switch pulls to ground to generate the pulses.
     

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  14. gIGoN

    gIGoN Probationary Member

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    None. Based on reading in the link ecu. Theres no frequency at all coming out from that wire. Ive tried on 2 different clusters so i dont think the cluster meter is the issue though. Would there be anything else i hv missed or should check to get the reading?
     
  15. DSMPT

    DSMPT Proven Member

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    What you tested is only a wire between the cluster and the ECU. I see you are hacking the harness, so you should check all wiring related to the reed switch and the reed switch itself.
    Should check :
    - If the black wire in the green circle in the pic is surely grounded. (As you already tried another cluster, I doubt this first)
    - If the wire from ECU pin #66 has some voltage with a "stock" ECU connected. (As @steve asked you above. I think it's 5v but it could be wrong)
    - On the cluster side, insert a tiny flat head screwdriver to the hole where the speedometer cable goes in and turn it several times, while turning the screw driver check if there is continuity between the pin for the black wire in the green circle and the pin that goes to the ECU. If the reed switch in the cluster is working well, you would see continuity on and off.

    Another possibility is : now you mentioned that you are using Link ECU, this could be the same issue as AEM EMS Series 2 on 1G DSM that the ECU doesn't receive any pulses from the cluster. If so, just go with an external VSS.
    1.jpg
     

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  16. gIGoN

    gIGoN Probationary Member

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    Traced and all the black wires frm both blue and brown are conected together. Did a continuity test and all the wires are grounded fine. Not cuts on the wires or whatsoever.
     
  17. gIGoN

    gIGoN Probationary Member

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    I decided to open up the cluster and found this 2 pins which connects to the whole speedo section in the cluster meter:



    From the back of the cluster the 2 pins are tighten by 2 screws. Can i just connect a round ring terminal to these 2 screws? 1 goes to the ecu and one goes to the ground? Would that work?

     
  18. DSMPT

    DSMPT Proven Member

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    You are not reading what I said. I suggested to check 3 things.
     

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  19. gIGoN

    gIGoN Probationary Member

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    good news. i did the 3rd step u mentioned my reed switch is working fine, so what i did was i connected an ring connected to a wire to the screw on the top right (looking from behind the cluster) which is beside the left signal and pulled it directly to pin #66 and thank god it worked.

    my new issue now is that the reading is way off in link ecu. eg: on my speedo its showing 40km/h but in the ecu its around 20km/h. and sometimes it spiked for no reason, probably something to do with the grounding.
     
  20. DSMPT

    DSMPT Proven Member

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    I think what you are doing is directly applying some voltage. Which means this issue probably is caused by ECU side, the ECU is not providing the voltage. I don't use Link ECU so I am not sure, could be the VSS parameters or the ECU itself. What voltage did you apply? If you are applying 12v then try to apply 5v as I mentioned above and see if it works. Also try to play with VSS parameters in the software.
    This sounds like similar to the issue of AEM EMS series 2 on 1G. If you can't make it work properly with the VSS parameters, go with a terratrip speed sensor probe. With this method, you can still use the stock speedometer and you can have stable pulses to the ECU.
     

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