P0451 (W/O ORVR)

CIRCUIT DESCRIPTION
The DTC P0451 Fuel Tank Pressure (FTP) Sensor Performance diagnostic checks the accuracy of the FTP sensor signal. The fuel tank pressure sensor responds to changes in the fuel tank pressure or vacuum. The fuel tank pressure sensor signal voltage to the Powertrain Control Module (PCM) varies from a minimum of about 0.2 volts with pressure in the fuel tank to a maximum of more than 4 volts with low pressure in the fuel tank.

CONDITIONS FOR RUNNING THE DTC
^ The barometric pressure is more than 75 kPa.
^ The engine coolant temperature is -8 to +110°C (18-230°F).
^ The intake air temperature is more than -8°C (+18°F).
^ The fuel tank level is 25-75 percent.
^ The fuel tank pressure is more than or less than the atmospheric pressure.
^ The engine has been running at idle for at least 2 minutes.

CONDITIONS FOR SETTING THE DTC
The change in the fuel tank pressure is less than a specified value after completion of EVAP system leak test.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) after 2 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 3 consecutively passing trips without a fault present.
^ A history DTC clears after 40 consecutive warm-up cycles without a fault.
^ Perform the scan tool Clear DTC Information function in order to clear the DTC.

DIAGNOSTIC AIDS
Check for any of the following conditions.
^ A skewed fuel tank pressure sensor may cause 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.

If a DTC P0451 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure. I/M Evaporative Emission (EVAP) System Set Procedure

An intermittent malfunction may be caused by a fault in the fuel tank pressure sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions. Intermittent Conditions

If a DTC P0451 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

TEST DESCRIPTION

Steps 1-11:

Steps 12-18:

Steps 19-30:

The numbers below refer to the step numbers in the diagnostic table.
1. The Diagnostic System Check-Computers and Control Systems 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. Review Freeze Frame data in order to determine the condition of when the DTC set. Always record this information.
10. This step verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes. This also checks the sensor signal input circuit.
12. This step checks the operation of the fuel tank pressure control valve.
13. This step checks the operation of the fuel tank pressure control valve.
14. This step checks for a stuck EVAP canister vent valve or a clogged inlet air hose at the EVAP canister vent valve.
15. This step performs an EVAP canister vent solenoid test. The EVAP canister vent valve output control is disabled by the PCM when any DTCs are stored, when engine speed is present, or when the engine operating temperature is less than 80°C (176°F).
18. This step performs a control circuit test on the EVAP canister vent valve. The EVAP canister vent valve output control is disabled by the PCM when any DTCs are stored, when engine speed is present, and when the engine operating temperature is less than 80°C (176°F).