Signal voltage too high means that the sensor isn't changing state or signal is beyond the expected limit. Put a volt meter on the signal line when everything is connected then apply vacuum / low pressure. It is possible to have a power wire pinched to the signal wire.

You also need to look at where the is sensor gets pressure from, maybe there is a broken or clogged hose.

A MAP sensor has a ground , 5 V voltage supply and a signal out. Systems generally use 0.5 V as the floor and 4.5 V as the limit of signal range. If the computer sees voltage beyond these limits it will trigger a low / high code.

Also, have a look at live data though be aware that some systems will substitute in an expected value when a component fails so an actual volt meter on the wire is always a good test.