My speedometer works fine. My trimometer works fine. But the tach still does not work, which is okay for now. However, at some point I missed, the odometer stopped working. Can anyone tell me what drives it?

Thanks as always.

 

Generally the speedometer is run off of wheel speed sensors, or if there are no wheel speed sensors it will be run off the VSS (vehicle speed sensor) which reads the speed of the transmission output shaft.

The tachometer runs off of data supplied from the crankshaft position sensor. These instrument clusters are very well known to fail. You can pull the cluster apart and look for cracked solder points, if any are found to be cracked send the cluster out to a repair facility for around $100 usually. You can test the cluster inputs if you have an oscilloscope, sometimes a multimeter will work.

 

As I understand it, the tachometer is run off the alternator. See that thread elsewhere.

What I don't understand is how the speedo can work but not the odometer.

 

Well the tachometer is a reading of engine rpm… that wouldn’t ever receive data from the alternator, it would be from either the camshaft or crankshaft position sensor, likely the crankshaft position sensor, the voltage output reading wire from the alternator is likely what supplies your battery voltage reading to you instrument panel.


If your odometer and you tachometer are both not functioning try to smack the top of the dashboard and see if they temporarily return operation, if they do pull and replace the cluster.

 

Believe me, as a trained auto mechanic it surprised me too, because I always thought as you do. Didn't make sense, and still doesn't.

Anyway, I doubt hitting the top will make any difference because the truck is so bouncy anyway.