Help with low reference voltage!

[Georgehine]

I am trying to diagnose a -2.8 psi reading on my map sensor when the vehicle is not running. I thought the map sensor was bad so I started by testing the reference voltage to the map sensor. The reference voltage is 4.78 unplugged from the sensor and the vehicle battery voltage is 12.2 is the reference voltage the problem in this situation or is the battery voltage creating the low reference voltage. Thanks in advance

[amdriven2liv]

From my info the range for the Reference Volts is 4.5 to 5.5

Have you cleaned the MAP tube and the connection where it goes into the manifold?