Regardless if the voltage is high or low, you should check the sensor(s). Grab a volt meter and start poking around and refer to the owners manual or a repair manual for the approximate values of voltage/resistance. Make sure it isn't dirty as well and everything fits snug and there are no air leaks anywhere. That's the first place to start. It's best to have a good handheld so you can look at freeze frame data. Although not everyone has those since they are expensive, but they are awesome to have around in such a situation. I don't own a AP yet so I'm unaware of the info/detail they can give with diagnostic information.