P0451

DTC P0451

CIRCUIT 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 SETTING THE DTC
- The FTP voltage is less than 0.78 volts or more than 2.94 volts within 12 seconds of start up.
- The condition is present for more than 10 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 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.

TEST DESCRIPTION

Steps 1-4:

Steps 5-8:

Steps 9-14:

The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies that the condition is present.
4. This step tests the 5-volt reference of the FTP sensor.
5. This step tests the low reference circuit of the FTP sensor.