No speedometer....Speed Sensors??

Discussion in '80-Series Tech' started by bw86newman, Mar 1, 2017.

  1. bw86newman

    bw86newman

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    Hi everyone,

    This is my first post on here as an actual owner of a land cruiser.

    I just purchased a 1995 J80 from the original owner about a month ago. PO kept amazing care of the truck and there are a bunch of maintenance records to go with it....no wheeling, just a city car.

    Everything has been working fine (except a couple bulbs & the passenger seat) until today. Drove to work and the speedometer wasn't working (pinned at 0mph). After the car sat for about 2 hours, starting driving again and the speedometer was working. Then drove home from work and speedometer wasn't working again. Same issue.

    I have done a little research on this and it seems that the speed sensors could be faulty or issue with the wiring. One of my main questions is how many speed sensors are there? The FSM shows two front speed sensors (one by each wheel) and two rear speed sensors (one by each wheel). Are those the only four or is there one on the transfer case as well?

    Any tips/insight on this issue is greatly appreciated.

    Thanks
     
  2. RadarFJ40

    RadarFJ40

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    Speed sensor on t-case. 450 or so oem.
     
  3. Tedward

    Tedward 95 LC SILVER Star

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    Those four sensors are the Wheel Speed Sensors used for Anti-lock Braking System (ABS)

    Edit.....
    I deleted the rest of this post because it was all wrong. My bad! Didn't want all that wrong info to steer me and others off the path of least resistance.

    I have no idea what is wrong with your wagon, but it's not the wheel speed sensors causing your problem.
     
    Last edited: Mar 3, 2017
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  4. Tapage

    Tapage Club 4X4 Panamá SILVER Star

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    95 no speedo by cable ..
     
  5. baldilocks

    baldilocks Battle Ground, WA GOLD Star

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    Could you please post a clear photo of said speedometer cable? I can't seem to find mine.
     
  6. bw86newman

    bw86newman

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    Without digging around under the truck (will do that tomorrow), here is what I have found.

    VSS #1 plugs into the speedometer drive gear - 1995 TOYOTA LAND CRUISER SPEEDOMETER DRIVEN GEAR (ATM)

    The VSS #1 is this - 1995 TOYOTA LAND CRUISER METER and is located on the aft driver side of the transfer case seen here https://forum.ih8mud.com/attachment...9/?temp_hash=3d842e840ff0a6d77207d8aeb3f4f9e7 found this on a post by 'yota dawg'

    The VSS #2 is this - 1995 TOYOTA LAND CRUISER OVERDRIVE & ELECTRONIC CONTROLLED TRANSMISSION #89413B.

    As for the cable driven speedometer, there is a diagram here for the 1995 models - 1995 TOYOTA LAND CRUISER METER but no actual parts numbers, I think it was discontinued.

    Here is another thread regarding speedo issues and the VSS's. Someone states there that the cable driven speedo was discontinued after the 1993 models.

    Thanks for the replies and let me know what you guys think.

    Cheers
     
  7. baldilocks

    baldilocks Battle Ground, WA GOLD Star

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    There is no mechanical cable. The speed sensor on the transfer case sends a signal to the speedometer.
     
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  8. Flyin Tyes

    Flyin Tyes

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    I too have intermittent speed odometer issues in my 94. does your speedometer bounce or move while idling at a stop? I believe there are two speed sensors. there is also a cable going into the transfer case, but it doesn't connect to the cluster on mine. I have had my cluster out while trying to fix the issue.
    I replaced sensor #2 at the transfer case, but it didn't resolve the issue.
    I think my problem is a connection or wiring.
    If I mess with sensor #2 it will usually work right after I reconnect it. Lately it has been working when I first start it and then after a few miles it starts acting up.
    Frustrating.
     
  9. SmokingRocks

    SmokingRocks Buy it, build it, bash it... Repeat

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    IF your speedo is not reading / reading intermittently then the issue is with the cluster itself or the VSS on the transfer case.

    The VSS sends a square wave signal to the speedometer circuit board. It is common that the speedo board craps out, if you don't have a check engine light I would surmise that its your speedometer board. Does your cruise control work?

    You should read through my recent thread where I was trying to build a signal conditioner, turns out I didn't need it but you can find absolutely everything you ever wanted to know about this circuit in this thread.

    Need Help from Electrical Gurus
     
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  10. bw86newman

    bw86newman

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    Thanks for the input everyone. Driving today there was no action from the speedometer at all...I am hoping it is just a bad VSS #1 sensor. Don't really want to deal with the actual cluster. Just went for a drive to test the cruise control....works perfectly.

    @SmokingRocks ...does the speedometer not working but the cruise control is mean anything to you? (Read through your thread. to be honest, its a little over my head at this moment. Will need to do some rereading of circuits. hah)

    @Tedward stated that the VSS #2 runs the cruise control. Maybe it is the issue?
     
  11. SmokingRocks

    SmokingRocks Buy it, build it, bash it... Repeat

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    Dont worry I was terrified about electronics and didn't understand it at all. It was voodoo magic to me, I spent all my energy trying to not let the smoke out.

    So don't let this overwhelm you, electronics can be fun once you begin to understand it.


    The VSS outputs an Alternating Current signal +12v on then -12v then +12 then -12v. That is called a square wave here is the difference between a square wave and a sine wave (wall outlet AC 120V). The faster the vehicle rolls the faster the VSS generates the the on off pulses (increasing frequency). This is read by the speedo, cruise control and ECU all separately.
    [​IMG]

    So the tricky thing is that while the VSS sends a signal out to the combination meter its doing so though a transistor which is basically a switch.

    Now here is where you have to follow me. The ECU, Cruise Control module and TCM all have diodes in them which BLOCK voltage or signal from coming in. They instead put 12v OUT. This 12 volt current from the ECU's want to complete the circuit which means flowing backwards toward the speedo and VSS.

    Since there is a Diode in the ECU's they wont accept nor read a singal from the VSS. what the VSS is doing is turning off the ground on the tranistor which OPENS the circuit for the ECU's (ECU voltage out to VSS drops to 0volts) then when the VSS dips to -12v it allows the ECU voltage to pass through the ground on the transistor which completes the ciruit for the ECU. This makes translates the square wave signal 12v to -12 v from the VSS to a 12v to 0v signal read by the ecu.

    Here is an image of the VSS putting out its signal (+12v). Notice how it is blocking the ECU output voltage .
    [​IMG]


    Now this is how the circuit looks when the VSS is on its 'off' swing.
    [​IMG]

    Voltage flows from the ECU through he green lines through the transistor at the VSS out through the ground.



    So thats a long and probably incoherent explanation.... Sorry...

    If your cruise control works then you have an intact ground at one of your transistors. Which means your VSS is fine and your speedometer board is broken.
     
    Last edited: Sep 12, 2017
  12. Tapage

    Tapage Club 4X4 Panamá SILVER Star

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    There is a procedure described on the FSM about how to test the VSS ..?
     
  13. bw86newman

    bw86newman

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    Update....Driving today, the speedometer worked as it should normally. Strange. Maybe it is the VSS #1??

    @Tapage if you are asking, yes, there is a procedure on how to test the VSS #1. Here it is....

    Screen Shot 2017-03-03 at 6.07.43 PM.png
     
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  14. SmokingRocks

    SmokingRocks Buy it, build it, bash it... Repeat

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    You would need to buy, build or borrow an oscilloscope.

    If your cruise control is working then your VSS is fine. Do you have a check engine light?

    A bad VSS will trigger a check engine light and prevent your cruise control from functioning.
     
  15. bw86newman

    bw86newman

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    I am starting to understand your explanation and diagrams....can you explain what the green and yellow lines are?

    We are talking about the VSS #1 on the transfer case, not the VSS #2 on the transmission. Correct?

    Also, one note. Ever since I bought the truck, there has been a 15 amp fuse for gage where is says there should be a 10 amp. Could this have contributed to any fault. I know it is not necessarily good to use larger fuses. My issue started when the 15 amp fuse was there....then I swapped it out for the 10 amp one (yesterday morning) and it didn't do anything, speedo still didn't work, but everything else worked fine. This morning, I double checked the 10 amp fuse with a fuse checker (not sure why, it was good) put it back in and then the speedo worked the rest of the day.

    It seems as though your insight keeps pointing to the speedometer itself.
     
  16. SmokingRocks

    SmokingRocks Buy it, build it, bash it... Repeat

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    The yellow dots show current, and the green traces that path. Those simulator diagrams aren't perfect the yellow dots should flow to the VSS's transistor then to the ground in the second image.

    Its a simple on off (1, 0) circuit essentially its a a simple computer, the ECU, cruise control and speedometer read the 1...0....1...0..1..0.1.010101 and translate it based on the frequency to "vehicle speed".

    Like I said if your cruise control works and you don't have a check engine light then your VSS is probably fine.
     
  17. Tapage

    Tapage Club 4X4 Panamá SILVER Star

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    My speedo it's going up ( Cruiser stopped ) and down randomly sometimes I get to speed ( like 40 or so ) and my speedo said I'm going 20 ..
     
  18. SmokingRocks

    SmokingRocks Buy it, build it, bash it... Repeat

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    Your issue is more than likely the same as the OP's. Read through the thread.
     
  19. ampline

    ampline

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    Did you ever figure out your speedo issue? I'm trying to fix mine now,, my problem is exactly like yours. However all the posts I've researched on this topic just end without the "fix" being mentioned.. thanks in advance...
     
  20. SmokingRocks

    SmokingRocks Buy it, build it, bash it... Repeat

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    does your cruise control work?

    YES ---> REPLACE INSTRUMENT CLUSTER
    NO-----> VERIFY CONTINUITY BETWEEN CLUSTER AND VSS
    • IF CONTINUITY PASSES INSPECT / REPLACE VSS
    • IF NO CONTINUITY TRACE WIRE HARNESS UNTIL BREAK IS FOUND
     
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