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Freightliner Problems

Discussion in 'Trucks [ Eighteen Wheelers ]' started by WildHog, Oct 22, 2011.

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  1. Oct 22, 2011 #1
    WildHog

    WildHog Light Load Member

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    95 Freightliner COE No speedometer and no Cruise Control.
    I see a sensor on the front and back of the transmission. Is it the one on the back?
     
    WildHog, Oct 22, 2011
    WildHog, Oct 22, 2011
    #1
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  3. Oct 22, 2011 #2
    mgfg

    mgfg Road Train Member

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    The one on the rear is typically the speedo sensor.

    I can disconnect my speedo and my cruise still works on my '05 KW.
     
    mgfg, Oct 22, 2011
    mgfg, Oct 22, 2011
    #2
  4. Oct 22, 2011 #3
    Heavyd

    Heavyd Road Train Member

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    Yep, try replacing the one on the back. The front one will be be for the tach.
     
    Heavyd, Oct 22, 2011
    Heavyd, Oct 22, 2011
    #3
  5. Oct 22, 2011 #4
    WildHog

    WildHog Light Load Member

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    Tach works fine. I've read somewhere in my searching that the Back sensor is the same as the Crankshaft position sensor. (4 wire) Can one of the excellent mechanics here confirm that? I have that part number as I just replaced that sensor.
     
    WildHog, Oct 22, 2011
    WildHog, Oct 22, 2011
    #4
  7. Oct 22, 2011 #5
    Heavyd

    Heavyd Road Train Member

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    No, the back sensor on the trans with the 4 wire sensor is all for speed. One pair feeds the speedo, and the other pair feeds ECM.
     
    Heavyd, Oct 22, 2011
    Heavyd, Oct 22, 2011
    #5
  8. Oct 22, 2011 #6
    WildHog

    WildHog Light Load Member

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    No, what I meant to say are the two sensors the same part number? I know they are both 4 wire sensors.
    I know they don't do the same things. I read somewhere that you could use this sensor mounted on the transmission to test with if you suspected the crank sensor was bad.
     
    WildHog, Oct 22, 2011
    WildHog, Oct 22, 2011
    #6
  9. Oct 23, 2011 #7
    Pablo-UA

    Pablo-UA Road Train Member

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    '95 FLA is really old truck, so I'd check for wiring issues. The weak spot is under cabing chassis to cab wiring harness. Cab rocks on frame so wires may easily be broken. In Russia so old rigs may got wiring and connection corrosing issues with Moscow road solt. Very corrosive thing.

    Sometime only one pair of VSS wiring is used, to ECM only and speedo works getting data from J1708 (j1939 appeared in 98 )
     
    Pablo-UA, Oct 23, 2011
    Pablo-UA, Oct 23, 2011
    #7
  10. Oct 23, 2011 #8
    Heavyd

    Heavyd Road Train Member

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    Oh, ok, I see, yes it should be about the same, I think you can switch them for testing.
     
    Heavyd, Oct 23, 2011
    Heavyd, Oct 23, 2011
    #8
  11. Oct 23, 2011 #9
    WildHog

    WildHog Light Load Member

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    Ok, thanks guys I try and check out the wiring. This truck has been used very little but there is some rust on it. Not a tremendous amount. What is this J1708?
    I wish I could get a schematic of the truck wiring.
     
    WildHog, Oct 23, 2011
    WildHog, Oct 23, 2011
    #9
  12. Oct 23, 2011 #10
    Heavyd

    Heavyd Road Train Member

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    J1709 is a pair of wires in between electronic components for communication and data transfer. It is a data link for things like the ECM and ABS ECU to talk to each other with. In modern trucks the ECM gets a signal from the speedo sensor, conditions and processes it into a usable value then sends the data over 1708 to the cluster to tell the speedo what speed you are going. 1939 is basically the same thing, but faster data speeds. Older trucks with dash clusters that did not get the data from the ECM over the 1708 would get the data from the speedo sensor itself. The sensor would have two separate leads, one for the ECM and one for the cluster.
     
    Heavyd, Oct 23, 2011
    Heavyd, Oct 23, 2011
    #10
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