Western Star Gauge Problem-This is Bizarre!

Discussion in 'Western Star Forum' started by 04 LowMax, Feb 16, 2014.

  1. 04 LowMax

    04 LowMax Medium Load Member

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    04 WS. Pyrometer started reading crazy high temps a while back, eventually stays pretty well at max all the time. Suspected sending unit, replaced it, same thing. Thinking it must then be the dash gauge, got a new one and tried it today, no change. In taking a close look at the wires on the gauges, they are all wired in parallel. Huh! How can that work! The 3 wires, red, black, and yellow, run from one gauge to the next, and so on. If anyone could please explain how this works, I would be most grateful. I recall when taking a radio and tv course almost 30 years ago, how one conductor could share different types of information, using phase, ac, dc and different frequencies, but, if thats what they did here thats unusual in a truck. And, then, how do I go about trouble shooting this to get it to work...usually I can figure these things out pretty well, but I am at a brick wall on this one.
     
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  3. brian991219

    brian991219 Road Train Member

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    I am not positive on your Western Star as I have little experience repairing Western Star (plenty of experience on their sister brand Freightliner as well as International) but it sounds like a multiplexing system which has become common in most vehicles over the last decade, each gauge has a unique address, you do not actually get the signal from the sending unit directly to the dash it goes thru the VPM or ECM first then the data is sent over a common information bus to several different systems and points in the truck at the same time. Gone are the good old days where you can easily trace a problem, for this system you need a logic probe, computer that can read the data bus, and the factory programming for the signal so you know what you are looking for.
     
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  4. 04 LowMax

    04 LowMax Medium Load Member

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    Sounds like that might be the case here. I might just be better off putting in an old fashioned manual, direct feed gauge. Thanks.
     
  5. underpsi

    underpsi Road Train Member

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    look underneath the floor on your driver side from the firewall. You will see a box that the pyrometer probe wiring runs to. I've seen this being an issue on a couple trucks.
     
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  6. 04 LowMax

    04 LowMax Medium Load Member

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    Just had a thought, I wonder if I could hook the 2 wires from the sending unit direct to the gauge and totally bypass the ecm-multiplex portion? Brian or Kevin, what do you think?
     
  7. underpsi

    underpsi Road Train Member

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    I doubt it. I think the gauges are specific to the multiplex system and the only way you could do that is if you used the gauge from the prior trucks like in my 2000. The gauges still look the same
     
  8. 04 LowMax

    04 LowMax Medium Load Member

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    Yes, you were quite right. I ended up putting in an aftermarket, digital one with a blue display. Love it! Works from start up, easy to see, and seems very accurate. I would highly recommend it.
     
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  9. mr. Large

    mr. Large Bobtail Member

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    May 10, 2014
    Cumberland, Alberta
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    This sounds like the beginning to a ground problem. If you start experiencing problems with all your gauges, the likely culprit is corrosion to the ground wires from the cab to the starter or frame. Check the resistance diffference at the the firewall cluster in the engine compartment compred to the large wire at the starter or frame ground.
     
  10. Roccon31

    Roccon31 Bobtail Member

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    May 30, 2013
    bucks co, PA
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    YUP. what he said. go over ALL connections between batteries, frame, starter, everything. also, those data boxes DO go bad. dealer can check it for you. the solution you found by using a mechanical gauge is certainly the easiest.
     
  11. Cummins Fanboy

    Cummins Fanboy Bobtail Member

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    I have a 2006 western star 4900sa, i am having issues with all the gauges not working, all of the grounds appear good and the gauges will light up and make the sound like they are cycling but none move except for air gauges because of air line pressure to the gauge. i am getting 4.7v on the signal wire to the gauges, im wondering if there is a ground somewhere that i am over looking does anyone happen to know were the gound for the gauges is located. We have spent a week banging our heads against a wall trying to figure this out. (Gauges worked fine untill we sent the truck to get painted, only thing we know is they unhooked the batteries, pulled the doors off and pulled off the hood. they climbed around the engine bay to paint the top of the cab but all connections look to be good. Gauges haven't worked since truck left the paint shop)
     
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