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.
Western Star Gauge Problem-This is Bizarre!
Discussion in 'Western Star Forum' started by 04 LowMax, Feb 16, 2014.
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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.
Jubal Early Times, Dino soar, Hammer166 and 3 others Thank this. -
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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.
04 LowMax Thanks this. -
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?
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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
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Cetane+ Thanks this.
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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.
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