Maybe these will help you. I'd pull the vehicle harness and ohm across 556 and 557 to start. Should be 700-1300'ish, IIRC.
Make sure that is good, then move on to the data link. Just takes a few minutes, and is easy. Also look at the individual female terminals for 556 and 557. It is very common for the spring to lay back and not make good connection.
Then you'll know Vss Wiring is good. 2 lead sensors, and 2 sensor systems used one of those leads to drive the speedo.
Most later trucks the speedo waa driven by an output from the ECM, but my 98 DDEC 4 is also is a 2 sensor system.
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2015 Coronado - No Speedo or cruise control
Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by dberset, Jan 4, 2025.
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Rideandrepair, dberset, BoxCarKidd and 1 other person Thank this.
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I did repin 556 and 557 because the very first thing I thought of was loose pins. Resistance was the same at the ECM connector as at the sensor connector. Speed signal is coming from somewhere. My scangauge reads road speed through the 9-pin. In my head I think the problem is between the ECM and cluster. I don’t know how or where to start. I’m assuming that the wires go to multiple places throughout the truck including the cluster. No idea what to look for to confirm the circuits are good.
Big Road Skateboard Thanks this. -
dberset Thanks this.
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So now what does the range selector in the transmission have to do with the speedometer?
I changed the shifter boot so I don’t lose any toes to frostbite and when I aired up the truck to make no air was leaking, I was moving the range selector up and down and the speedometer started jumping and fast idle shut off. I was able to duplicate it many times. every time it shut off my fast idle.
Is my issue something as stupid as a loose yoke? It doesn’t move around like it’s loose. And I can’t turn the tone ring. -
Rideandrepair Thanks this.
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BoxCarKidd Thanks this.
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When you replaced the vss, did you bottom it out? Only needs to be backed off a tiny amount, so it’s not in full contact, I’m sure you did.
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My opinion....ohm testing wire circuits is pretty pointless as one single strand of wire will show it to be good. Make some load test lights with a 9004 style bulb or even a 1156 bulb and see if the circuit can power a load.
RocketyMan Thanks this. -
Good point.IH9300SBA Thanks this.
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