No power to speed sensor

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When dealing with vehicle speed sensors, it's important to know what sort of truck is involved. Some run 2 sensors - 1 for the ECM and 1 for the speedometer. Some trucks run 1 sensor to the gearbox controller, then the cab and ECM read it on the data link. Some run 1 sensor to the ECM and the body control module read it on the data link.

If the sensors are inexpensive, I'd try changing it and inspecting the pins on the connector. If it's the adjustable type - Turn it all the way in and 1/2 turn out (they are often very easy to break if the locknut is over tightened). If that doesn't work, you'll need to chase the wiring and potentially start looking at changing the speedometer itself.