It is quite easy to get at and a cheap part to replace.

You will need to remove the alternator cover on the left hand side of the engine. You will immediately see the sensor. It is held in place by two bolts. The bolts can become loose causing erratic readings, so check that first. Also the sensor head can get fouled up, so check that too. Otherwise replace it.

Before you remove the cover, you can check the resistance at the two pin connector if you follow the wiring up from the casing. I don't know off hand what it should be though. I'll see if I can look it up for you?

__________________