I have a 1998 Isuzu Hombre (2wd) 2.2L. My "Service Engine Soon" light came on yesterday. I had the code checked at the local autozone store and it came back with P0452 EVAP Emission Control System Pressure Leak Sensor Low. What does this mean?

Also, as an FYI, I had my fuel pump replaced in Oct. 2007

Thanks.

Circuit Description
The Fuel Tank Pressure sensor is used in order to detect a vacuum decay or an excessive vacuum during the EVAP diagnostic routine. The Fuel Tank Pressure sensor responds to the changes in the fuel tank pressure or vacuum. The signal voltage to the Powertrain Control Module (PCM) varies from a minimum of about 0.2 volts with pressure in the fuel tank to above 4.0 volts with a high vacuum in the fuel tank.
The Fuel Tank Pressure display on the scan tool has an auto zero feature which occurs at each ignition cycle and is corrected according to the barometric pressure. Because of this, the Fuel Tank Pressure may not accurately reflect the actual output of the sensor or the conditions within the fuel tank.

Conditions for Setting the DTC
The Fuel Tank Pressure Sensor voltage is lower than 0.1 volt for greater than 25 seconds.

Check for the 5 volt reference on the gray wire with the key on.
If you don't have that 5V Ref, you need a PCM.