It's a sensor inside the distributor. If you happen to have another distributor, the best way to check it is to replace the whole distributor, then you know if the wiring is ok and if the sensor is bad.
No you don't have to, you could get a replacement from honda, but may times it is easier to find another distributor, and probably cheaper. I am only saying that if you have another distributor, give that a try to diagnose the problem first. Even if you have a freind that has one, borrow his and try it out. If you want specific info on how to test the sensor try a helms manual. I would first diagnose the problem, and make sure that your timing belt is aligned properly, before worrying about replacing stuff.
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