Ron J is right on target with his post,

You might have a bad solder joint in the speedometer head. Most likely to the stepper motor that drives the odometer.

If you go to Art Bienstein's web sight cleanflametrap.com. I think he has great directions on repairing that problem, if its part of the code problem.

I suggest reflowing ALL the solder connections that you can do in any case. Especially the wiring harness connection on the board.

The specifications Ron mentions is the sensors total range of operation extremes. You will most likely never see that on a meter as their responsing sample times may not be fast enough to display it.

I have a special sensor tester made by Actron and it does not all ways hits the limits and it has a visual LED displays. It even has two that average the readings. Flashing only one of ten single LEDS are faster than making each segmented numeral separately up and down the scale.

The most important thing to take from both our statements is that you see the sensor fluctuations in a mid range area.

Good luck at retracing.

Phil