P0451

Schematic:

The evaporative emission (EVAP) system is used to store fuel vapors as to reduce the amount of unburned fuel from escaping into the atmosphere. The function of the fuel tank pressure (FTP) sensor is solely for EVAP leak diagnostics. The fuel tank pressure sensor is a transducer that varies resistance according to changes in fuel tank pressure (difference between fuel tank and outside air pressure). The ECM measures the signal voltage from the fuel tank pressure sensor, which is a reduced value of the ECM 5 volt reference. The signal voltage will read high when the pressure in the fuel tank is low (vacuum) and will decrease as the pressure in the tank increases. DTC P0451 will set if the fuel tank pressure sensor signal voltage at the ECM is above or below a calibrated voltage value considered unrational.

DTC PARAMETERS
DTC P0451 will set if fuel tank pressure sensor signal voltage is less than 0.78 volts (greater than 6.75 mmHg [3.61 in H2O]) or greater than 2.94 volts (less than -13.50 mmHg [-7.23 in H2O]) when:
^ Condition exists for longer than 10 seconds
^ Startup ECT less than 35°C (95°F)
^ Engine speed is at idle
^ Engine run time is between 1 and 12 seconds
^ EVAP diagnostics are not running
^ No low or high voltage FTP sensor circuit DTCs have been set

OR

DTC P0451 will set if fuel tank pressure sensor signal voltage is less than 0.78 volts (greater than 6.75 mmHg [3.61 in H2O]) or greater than 2.94 volts (less than -13.50 mmHg [-7.23 in H2O]) when:
^ Condition exists for longer than 1 second
^ Measurement is taken just before the start of the EVAP diagnostic system test. Refer to DTC P0440 for the enable criteria. P0440
^ No low or high voltage FTP sensor circuit DTCs have been set

DTC P0451 diagnostic runs once per ignition cycle once the above conditions have been met.

P0451 is a type B DTC.

DIAGNOSTIC AIDS

IMPORTANT: If DTC P0452 or P0453 is also set, diagnose that DTC first.

FTP SENSOR on Scan tool should read between 1.40 and 1.60 volts with ignition On, engine Off and fuel cap removed. This represents atmospheric pressure or 0 inches of vacuum.

DTC P0451 indicates that the fuel tank pressure sensor signal voltage is skewed high or low. Possible causes of DTC P0451:
^ Corrosion in the fuel tank inline harness connector
^ Corrosion in the fuel tank pressure sensor harness connector
^ Fuel tank pressure sensor skewed

IMPORTANT: In accurate readings will occur if resistance measurements are taken on a fuel tank pressure sensor. The fuel tank pressure sensor contains an internal amplifier circuit that requires applied voltage to function properly.