Engine speed and engine position sensors. I have a '99 ISC350E with 44k miles. The coach is now at Cummins and a "Wellness Check" indicated they need changing. This is the 3rd time it's been to Cummins (since new) and each time they say these sensors need changing. What do they do and how can an owner tell if they are bad?
If these sensors do indeed go bad frequently, should I be carrying spares?