P0451
DTC P0451CIRCUIT DESCRIPTION
The control module monitors the fuel tank pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the evaporative emission (EVAP) diagnostic test. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. If the FTP sensor signal voltage is not within a calibrated value range during a cold engine start, this DTC sets.
The table illustrates the relationship between FTP sensor signal voltage and the EVAP system pressure/vacuum.
CONDITIONS FOR RUNNING THE DTC
The start up ECT is less than 33°C (91°F).
CONDITIONS FOR SETTING THE DTC
- The FTP voltage is more than 4.5 volts.
- The condition is present for more than 3 seconds.
ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
CONDITIONS FOR CLEARING THE DTC
- 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 non-emission related diagnostic.
- Clear the DTC with a scan tool.
DIAGNOSTIC AIDS
IMPORTANT:
- If DTC P0452 or P0453 are also set, diagnose that DTC first.
- Inaccurate readings will occur if resistance measurements are taken on a fuel tank pressure sensor. The fuel tank pressure sensor contains an internal amplifier circuit that requires applied voltage to function properly.
- The FTP sensor on the scan tool should be between 2.35-2.85 volts with the ignition ON and the engine OFF and the fuel cap removed. This represents atmospheric pressure, or 0 inches of vacuum.
- DTC P0451 indicates that the fuel tank pressure sensor signal voltage is skewed. Possible causes of DTC P0451 are as follows:
- Corrosion in the fuel tank inline harness connector
- Corrosion in the engine I/P inline harness connector
- Corrosion in the fuel tank pressure sensor harness connector
- The fuel tank pressure sensor skewed
- For intermittent conditions, refer to Intermittent Conditions. Intermittent Conditions
TEST
