Speed sensor...

Discussion in 'Technical' started by geron, Jun 6, 2016.

  1. geron

    geron National Petroleum Equipm

    Hey Guys,
    I seriously need some help with this electrical gremlin which is doing my head in.

    My Z has an issue where it does not show up the speed on Consult or Datascan even though the speedometer needle works each and every time the car moves!
    As a consequence of this, 3 things happen.
    - Steering goes heavy after about 5 minutes of driving
    - HICAS light lights up after another 5 minutes of driving
    - Cruise control cannot be set at any speed when speedometer is over 60km/h.

    Initially, I thought this might be a HICAS issue and have spent since Saturday, car on hoist, performing in depth diagnosis as per the Z32 Manual & combination of Conzult & Multimeter. All solenoids are of the correct resistance. Nothing comes up except that the voltage on the speed sensor is hanging around 1.1v & doesn't oscillate b/w 0 and 5v when turning the wheels as suggested in the manual. It just sits around the 1.1v mark.

    Once I realised that the ASCD (cruise control) could not be set at any speed over 60km/h, I realised that the diagnosis is pointing to the speed sensor & associated wiring.

    While referring to the HICAS and ASCD sections of the manual, I investigated the path of the signals from the vehicle speed sensor from the g/box to the HICAS & ASCD CTRL Units to see how this all works and to see if there is any broken circuits along the way that might be causing any issues.

    Basically, the two wires are Y/B(B=Black) & Y/L(L=Blue) that are at the Vehicle speed sensor plug at the g/box. Following those, they go all the way to the Instrument Cluster. Then there is a 3rd wire Y/G which comes off the Instrument Cluster which is the signal to all the CTRL Units. So this wire goes to the ASCD, HICAS and Engine CTRL Units.
    I have checked continuity between the Y/G wire from the dash to each ECU type and there is continuity! (To my surprise). Even pin 53 on the Engine ECU.

    I also checked the resistance of the Vehicle speed sensor all the way to the Instrument cluster and 0.24...ohms. I have another Z32TT Vehicle speed sensor off the car and get the exact same resistance. This tells me there is continuity all the way back to the Vehicle speed sensor.

    So, now I'm lost with this.
    - There is full continuity between the Vehicle speed sensor and ALL the CTRL Units.
    - The speed of the vehicle is displayed on the instrument cluster without fail when the car is driven.
    - even though, there is no speed displayed on Datascan or Conzult.

    Can someone please share some light on this, I don't know what more to do.
    Should I change the Engine ECU?
    I was thinking maybe the Vehicle speed sensor, but the speedo works. What is going on?

    Peter
     
  2. geron

    geron National Petroleum Equipm

    The suggestions are overwhelming....

    So I have taken the speedo and ECU to the local TV Technician to look for cold solder joints and make them hot again.

    Within 2 seconds he spotted a few cold joints on the speedo PCB.

    It will be interesting to see how this goes, I can't wait to see what eventuates once everything is back in.
     
  3. East Coast Z

    East Coast Z Well-Known Member

    O'Connor Television?
     
  4. geron

    geron National Petroleum Equipm

    Coast Care Video TV in West Gosford.

    They have repaired a few ECUs, so the guy I spoke with, didn't look too fussed about it. Very common problem he said.
     
  5. geron

    geron National Petroleum Equipm

    Closure on this one...

    Just for anyone who has any interest as to what happened and to provide closure to this ordeal...

    This is what I discovered. The HICAS and the Cruise Control and power steering solenoid all rely on the speed signal that comes from the VSS at the back of the gearbox and goes to the instrument cluster which the signal is converted to something that the various CTRL Units can understand.

    Usually, If Consult or Datascan does not display a speed reading while the vehicle is moving, there is something wrong with the vehicle speed sensor wiring, somewhere.

    Anyway, the cause of my problem was the OBD/USB adaptor itself, of all things. For some reason, it caused havoc with the speed signal when installed making all CTRL units thinking there was no signal. All other parameters worked but not the speed signal. So, No HICAS, No Cruise Control, No signal to ECU and HEAVY steering.

    Who would have thought.

    I removed the OBD/USB interface and plugged in the Serial Interface to the OBD port and the computer and ran Datascan and Conzult and got speed signal straight away!!!! Drove the car around and no problems whatsoever.

    It must have been a faulty unit. It's like using an instrument to do analysis but the instrument itself is faulty providing the wrong information.

    So glad I got to the bottom of this. Having said that, it wasn't an absolute waste of time but an opportunity to obtain in depth knowledge of how the various systems in the Z work, which could come in handy in the future.
     
    pmac likes this.
  6. Harleynissan

    Harleynissan AussieSpeedingFines

    Amazing!

    Glad you got it sorted.

    I have similar problem with pain. Original injury is healed, but damaged nerve says it not.
    Pain can be handy, but what to do when the feedback loop is broken?

    Wish I had a serial connection I could use for my back, instead of my broken USB interface ;-)
     
  7. tuff

    tuff Member

    Someone sticky this frigging post, i just had the exact same problem I've been chasing for 2 whole days, bloody usb dongle at fault. GERON you are a legend mate, just sorted my problem
     
    geron and pmac like this.
  8. geron

    geron National Petroleum Equipm

    Thanks tuff, I'm glad this information was helpful. These OBD/USB interfaces are a waste of time on a Z32 and it's false advertising, since they don't work on all cars designed with OBD.
    I purchased two units thinking one was faulty with exactly the same results.
    I threw them in the Rubbish.
     
  9. geron

    geron National Petroleum Equipm

    There's also another post that I put up explaining which OBD dongles work and using Android with Datascan.
    It's here somewhere for anyone interested.
     

Share This Page