Circuit Description
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, the 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 low when the
pressure in the fuel tank is low (vacuum) and will increase as the pressure in the
tank increases. DTC P0451 will set if the fuel tank pressure sensor signal
voltage at the ECM is above a calibrated voltage value considered unrational.
Conditions for Setting the DTC
DTC P0451 will set if the fuel tank pressure sensor signal voltage is
greater than 4.5 volts, 18.75 mm Hg (10.04 in H2O)
when:
| • | The condition exists for longer than 3 seconds. |
| • | The startup ECT is less than 33°C (91°F). |
| • | The engine speed is at idle. |
| • | The engine run time is greater than 10 seconds. |
DTC P0451 diagnostic runs once per ignition cycle once the above conditions
have been met.
DTC P0451 is a type B DTC.
Diagnostic Aids
Important: If DTC P0453 is also set, diagnose that DTC first.
FUEL TANK PRESSURE SENSOR on the scan tool should read between 2.35-2.85 volts
with the ignition ON and the engine OFF and the 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. Possible causes of DTC P0451:
| • | Corrosion in the fuel tank inline harness connector |
| • | Corrosion in the engine I/P inline harness connector |
| • | Corrosion in the fuel tank pressure sensor harness connector |
| | Important: Inaccurate 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.
|
| • | Fuel tank pressure sensor skewed |
