P0451

CIRCUIT DESCRIPTION




The DTC P0451 Fuel Tank Pressure (FTP) Sensor Performance diagnostic checks the accuracy of the FTP sensor signal. Emission laws require that the powertrain control module (PCM) detect any leakage within the EVAP system. The PCM tests the EVAP system for leaks by monitoring the vapor pressures in the fuel tank with the FTP sensor. The FTP sensor contains a silicon based chip that changes electrical resistance when pressure is applied. The PCM supplies a 5-volt reference, an electrical ground, and a signal return circuit that has a 5-volt bias. The FTP sensor signal voltage varies from a minimum of about 0.2 volts with negative pressure in the fuel tank, to a maximum of more than 4 volts with positive pressure in the fuel tank.

CONDITIONS FOR RUNNING THE DTC
- DTC P1450 and DTC P1451 are not set.
- The barometric pressure (BARO) is more than 75 kPa.
- The engine coolant temperature (ECT) is between -8°C to +110°C (18-230°F).
- The intake air temperature (IAT) is between -14°C to +70°C (7-158°F).
- The fuel tank level is between 25-75 percent.
- The FTP 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 fuel tank pressure is less than -40.0 mm Hg (-21.41 in H2O) or more than 40.0 mm Hg (21.41 in H2O) for 5 seconds.

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 the following conditions:
- A skewed FTP sensor may cause DTC P0451 to set. Compare voltage readings with a known good sensor.
- Inspect for obstructions and restrictions in the vapor passages that flow to the FTP sensor. Conditions that affect the pressure reaching the FTP sensor can cause a DTC P0451 to set.

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 1-4:

Steps 5-9:

Steps 10-12:

Steps 13-16:

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. The FTP sensor reading indicated on the scan tool will vary with the surrounding barometric pressure.
8. The FTP sensor voltage will vary with the surrounding barometric pressure.
9. This step verifies that the FTP sensor is able to react to evaporative emission (EVAP) system pressure changes.
11. This step checks for a blockage or a restriction that can trap pressure inside the fuel tank.
15. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0451 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P0451 appears in the Not Ran Since Code Cleared list, the P0451 diagnostic has not yet run. When DTC P0451 does not appear in the Not Ran Since Code Cleared list, the P0451 diagnostic has run. If the MIL is NOT illuminated and there is no Pending DTC Status in DTC Information, the P0451 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.