Tach Drive Speed Sensor

[Andyrv6av8r]

My tach went bonkers yesterday pegging out full rpm . Odd thing is, it did the same thing about a year ago and replacing the tach speed sensor fixed it. What breaks in these things and can they be checked or repaired? Do they serve any other purpose ,such as transmission control, in my 1045A2?

 

[Andyrv6av8r]

So I replaced the sensor again with a new one and the tach is back to normal working fine. Sensors seem to be doubling in price so I was hoping someone had some input on how to fix my problem.