P0451

Diagnostic Chart:

Wiring Diagram:

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 from a minimum of about 0.2 volts with pressure in the fuel tank to above 4 volts with a high vacuum situation in the fuel tank (vent solenoid stuck closed).

Conditions for Running the DTC

^ Engine coolant temperature between 70°C (158°F) and 110°C (230°F).

^ Intake air temperature between -10°C (14°F) and 50°C (122°F).

^ Barometric pressure greater than 75 kPa.

^ Fuel tank level is between 25 and 75%.

Conditions for Setting the DTC

^ Engine running at idle for at least two minutes.

^ Fuel tank pressure is lower than specified value after completion of EVAP system leakage check.

Action Taken When the DTC Sets

^ The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC

^ The MIL will turn OFF after three consecutively passing cycles without a fault present.

^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.

^ DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed.

Diagnostic Aids

Check for any of the following conditions:

^ A shifted (incorrectly calibrated) fuel tank pressure sensor may cause a 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 (LT. GRN/BLK wire).

^ When a DTC P0107, P0122 and P0450 are set together check for an open reference circuit (LT. GRN wire).

^ A poor connection at the PCM. Inspect the harness connectors for backed out terminal, improper mating, broken locks, improperly formed or damaged terminals, and a poor terminal to wire connection.

^ A damaged wiring harness. Inspect the wiring harness for damage and repair as necessary.

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.

If any wiring repairs need to be made, Refer to Repair Procedures in Electrical Diagrams.

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. Determine if a fault is present. Review Freeze Frame data to determine the condition of when the DTC set. Always record this information.

10. Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes. This also checks the sensor signal input circuit.

12. Checks the operation of the fuel tank pressure control valve. For additional functional checks, Refer to Enhanced Evaporative Emission (EVAP) System. Evaporative Emissions System

13. Checks the operation of the fuel tank pressure control valve. For additional functional checks, Refer to Enhanced Evaporative Emission (EVAP) System. Evaporative Emissions System

14. This step checks for a stuck EVAP canister vent solenoid or a clogged EVAP canister vent solenoid Inlet air hose.

15. An EVAP canister vent solenoid test. The EVAP canister vent solenoid output control is disabled by the PCM until the engine has reached a normal operating temperature of at least 80°C (176°F) and there is no RPM. Output controls can be found on the Tech 2 scan tool under Special Functions.

18. An EVAP canister vent solenoid control circuit test. The EVAP canister vent solenoid output control is disabled by the PCM until the engine has reached a normal operating temperature of at least 80°C (176°F) and there is no RPM. Output controls can be found on the Tech 2 scan tool under Special Functions.