Fuel Tank Pressure Sensor.

Anybody ever have to change one of these? I was looking at Alldata'* 2003 Bonneville freeby instructions and it says their is an access door in the rear compartment. They mean the trunk floor right? They also say I need to have 5 volts at the connector. I borrowed my neighbor'* volt meter and I'm going to see what I get. He said I should have 5 volts at the grey & black wire and to back probe the third wire for 2.5 volts.

Question: How do you back probe a connector? :?

2000 LeSabre

Edit: Ok I did some checking; apparently it is a 3-pin sensor with the mating 3-port connector.

Port A = low voltage reference
Port B = signal voltage of 0.1V to 4.9V (Depending on tank pressure)
Port C = 5 volt reference from the PCM

Question: Should I have 5 volts between A and C ?

Question: The back probe check is for the signal voltage out of Port B right? And you would do this with the sensor connected to the connector right?

Also from Alldata...

The Fuel Tank Pressure (FTP) sensor measures the difference between the air pressure (or vacuum) in the fuel tank and the outside air pressure.

The sensor mounts at the top of the fuel tank sending unit. The PCM supplies a 5 volt reference voltage and ground to the sensor. The sensor provides a signal voltage between 0.1-4.9 volts to the PCM. When the air pressure in the fuel tank is equal to the outside air pressure, such as when the fuel fill cap is removed, the output voltage of the sensor will measure 1.3-1.7 volts .

When the air pressure in the tank is 4.5 inches H2O (1.25 kPa ), the sensor output voltage should measure 0.5 + 0.2 volts (1.25 kPa) .

The sensor voltage increases to approximately 4.5 volts at -14 inches of H2O (3.75 kPa ).

Yes, measure between A and C for 5 volts, and then measure between A and B for the signal voltage. The connector will have to be attached to get a reading at B.

Thankyou Archon!!!