P0451
DTC P0451
DTC DESCRIPTOR
DTC P0451
Fuel Tank Pressure (FTP) Sensor Performance
DIAGNOSTIC FAULT INFORMATION
IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection
TYPICAL SCAN TOOL DATA
FTP Sensor Voltage:
CIRCUIT/SYSTEM DESCRIPTION
The fuel tank pressure (FTP) sensor measures air pressure or vacuum in the evaporative emission (EVAP) system. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal voltage varies depending on EVAP system pressure or vacuum. The controller also uses this FTP signal to determine atmospheric pressure for use in the engine-off small leak test, DTC P0442. Before using this signal as an atmospheric reference it must first be re-zeroed.
CONDITIONS FOR RUNNING THE DTC
- DTC P0451 runs only when the engine-off natural vacuum small leak test, P0442, executes.
- The number of times this test runs can range from 0-2 per engine-off period. The length of the test can be up to 10 minutes.
CONDITIONS FOR SETTING THE DTC
This DTC will set if the controller is unable to re-zero the FTP sensor voltage within a calibrated range during the engine-off small leak test, P0442.
ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.
DIAGNOSTIC AIDS
- A restriction in the EVAP canister or vent lines could prevent fuel vapor pressure from bleeding off fast enough. If the vent system cannot bleed off pressure fast enough, the re-zero procedure may not complete successfully, which could cause this code to set. By using the purge solenoid command on a scan tool, vacuum can be applied to the system instead of pressure. With the EVAP canister vent solenoid valve open and the EVAP canister purge solenoid valve commanded to 100 percent, the vacuum should not increase to more than 9 inches H2O.
- Ensure that the reference port on the FTP sensor is unobstructed.
- An FTP sensor that is skewed or does not have a linear transition from low to high may cause this code to set. Scan Tool Output Controls, Snapshot, and Plot functions can help detect erratic sensor response. To test the sensor signal under vacuum conditions, use the Quick Snapshot and the Purge/Seal functions to capture data while commanding purge to 20 percent, then plot the data to look for erratic sensor operation. A similar test can be done for the pressure side of the sensor operation by applying pressure with the J 41413-200 while taking a snapshot.
- A full fuel tank may cause misdiagnosis.
- When using the electronic emission system tester (EEST) to apply pressure, you can regulate the amount of pressure by activating the remote switch ON and OFF while observing pressure in the EVAP system using a scan tool.
CIRCUIT/SYSTEM VERIFICATION
1. If DTCs P0452, P0453, or P0641 are set, repair those first.
2. With a scan tool, command the EVAP canister vent solenoid valve closed.
3. Command the purge solenoid to 30 percent.
4. Observe the FTP sensor voltage parameter as the vacuum increased to the abort limit.
5. The voltage should scale smoothly.
CIRCUIT/SYSTEM TESTING
1. Start the engine with the J 41413-200 connected to the fuel filler neck.
IMPORTANT: Refer to the J 41413-200 operation manual for detailed instructions.
2. Allow the engine to idle.
3. Use the Purge/Seal function to seal the system with a scan tool.
4. Command the EVAP canister purge solenoid valve to 30 percent.
5. Observe the vacuum/pressure gage on the J 41413-200 and the FTP parameter on the scan tool.
6. Allow the vacuum to increase on the gage of the J 41413-200 until it reaches approximately 16 inches H2O, or until the vacuum reached the abort limit on the scan tool.
7. Verify that the vacuum increases to the abort limit on the scan tool or more than 3.2 volts, and the value is closely similar between the scan tool and the vacuum/pressure gage on the J 41413-200.
- If the values are not similar or the voltage did not reach 3.2 volts, replace the FTP sensor.
REPAIR INSTRUCTIONS
IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Fuel Tank Pressure Sensor Replacement
- Control Module References for powertrain control module (PCM) replacement, setup, and programming