P0451

Circuit Description
The fuel tank pressure sensor responds to changes in fuel tank pressure or vacuum. The fuel tank pressure sensor signal voltage to the PCM varies according to changes in fuel tank pressure. The voltage signal can range from a high of over 4 volts (pressure in the tank) to a low of 0.6 volts (high vacuum condition in the tank) when the vent solenoid is closed.

Conditions for Running the DTC
^ Engine coolant temperature is 70°C to 110°C (158°F to 230°F).
^ Intake air temperature is -10°C to 50°C (14°F to 122°F).
^ Barometric pressure is greater than 75kPa.
^ Fuel tank level is between 25 and 75%.
^ Engine has been running at idle for at least 2 minutes.
^ Fuel tank pressure is lower than a specified value after the completion of the EVAP system leakage check.

Conditions for Setting the DTC
The fuel tank pressure indicated is lower than a specified value after the completion of the EVAP system leakage check.

Action Taken When the DTC Sets
^ The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active.
^ The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC
^ The MIL turns OFF after three consecutively passing trips without a fault present.
^ A History DTC clears after 40 consecutive warm-up cycles without a fault.
^ Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC.

Diagnostic Aids
Check for any of the following conditions:
^ A shifted (incorrectly calibrated) fuel tank pressure sensor may cause a DTC P0451 to set. Compare voltage readings with a known good sensor.
^ A plugged sensor air vent hole. Inspect the sensor and clean if necessary.
^ When a DTC P0108, P0113, P0118, P0123 and P0450 are set together check for an open ground circuit.
^ When a DTC P0107, P0122 and P0450 are set together check for an open reference circuit.
^ A faulty electrical connection at the PCM.
For functional checks of the EVAP control system components, refer to EVAP Control System Diagnosis. Component Tests and General Diagnostics
An intermittent malfunction may be caused by a fault in the EVAP control system electrical circuits. Inspect the wiring harness and components for any of the following conditions:
^ Backed out terminals.
^ Improper mating of terminals.
^ Broken electrical connector locks.
^ Improperly formed or damaged terminals.
^ Faulty terminal to wire connections.
^ Physical damage to the wiring harness.
^ A broken wire inside the insulation.
^ Corrosion of electrical connections, splices, or terminals.
If a DTC P0451 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step determines if a fault is present. With the fuel tank filler pipe open to the atmosphere, the fuel tank pressure sensor should read near zero. The fuel tank pressure sensor reading will vary with changes in atmospheric pressure. The specified value in step 2, is typical of atmospheric pressure near sea level.
5. This step checks for a good fuel tank pressure sensor. A voltage that is within the specified value indicates that the fault is in the sensor input circuit or the PCM.
12. This step checks the operation of the EVAP canister vent solenoid. The EVAP canister vent solenoid output control is disabled by the PCM when any DTCs are stored, when engine speed is indicated, and until the engine has reached a normal operating temperature of at least 80°C (176°F).
15. This step checks for a stuck closed or internally blocked EVAP canister vent solenoid.
16. This step checks for a stuck open or leaking EVAP canister vent solenoid.