P0455

Schematic:

CIRCUIT DESCRIPTION
During specific operating conditions, the ECM performs various tests on the evaporative emission system. The system tests consist of the following series of events. After ensuring that the EVAP purge solenoid valve duty cycle has dropped to 0 percent, indicating that the valve is closed, the ECM commands the EVAP canister vent solenoid valve closed, sealing the system. The ECM monitors the accumulation of vapor pressure within the fuel tank via the Fuel Tank Pressure sensor. The EVAP test is aborted if the vapor pressure is too high. If any vapor pressure is measured, the pressure will be used later in order to compensate for a pressure reading during the small leak detection test. If a vacuum is measured which exceeds a calculated limit during vapor accumulation, DTC P0440 will set. The EVAP canister purge solenoid valve is then opened. Simultaneously, the Vent solenoid is opened. If the vapor pressure does not bleed off or bleeds off too slowly, DTC P0440 is set. Once the EVAP purge solenoid valve reached the desired position for the remainder of the diagnostic test, the Vent solenoid will be closed again. This causes a vacuum to be applied to the entire EVAP system. The ECM monitors the vacuum level within the system. If the desired vacuum level cannot be achieved, or if the vacuum level is reached but took too much time, DTC P0455 will set. Once the desired vacuum level is reached, the purge solenoid is closed, sealing the system. The ECM continues to monitor the Fuel Tank Pressure sensor signal, measuring the rate of vacuum decay. If the system holds vacuum, the vent solenoid is opened and the test is completed. In addition to the system tests, the ECM monitors the circuit integrity of the Purge solenoid (DTC P0443), the Vent solenoid (DTC P0446) and the Fuel Tank Pressure sensor (DTC P0450).

CONDITIONS FOR RUNNING THE DTC
^ Any of the following DTCs are not set: P0100, P0115, P0116, P0130-P0161, P0300-P0306, P0443, P0446, P0450, P0500, P0506, P0507, P0560, P1120 or P1220.
^ The vehicle speed is 0 km/h (0 mph).
^ The engine is at idle.
^ The Engine Coolant Temperature (ECT) at start is between -8°C (17°F) and 75°C (167°F).
^ Fuel system is in Closed Loop.
^ The engine load is less than 30 percent.
^ The Intake Air Temperature (IAT) is between -8°C (17°F) and 50°C (122°F).
^ The system voltage is more than 11 volts.
^ The engine run time is at least 17 minutes.
^ The secondary AIR system is inactive.
^ The secondary AIR system diagnostic is not running.
^ The short term fuel trim at the beginning of the test is more than -5 percent.

CONDITIONS FOR SETTING THE DTC
The EVAP system is unable to achieve vacuum or the time required to achieve vacuum is too long during the diagnostic test.

ACTION TAKEN WHEN THE DTC SETS
The ECM illuminates the Malfunction Indicator Lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes.
^ A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic.
^ The scan tool clears the MIL/DTC.

DIAGNOSTIC AIDS
The fuel tank assembly consists of an inner fuel tank, EVAP canister, ORVR system and the associated plumbing all encased within an outer fuel tank housing. The outer housing contains a tube that allows air between the inner tank and the outer housing to vent. A leak in any of the internal components of the fuel tank assembly will exit this vent. The vent is located in front of the fuel tank above the fuel filter. If a leak is detected by air exiting this vent while the EVAP system is pressurized, the fuel tank assembly will require replacement. The internal components of the fuel tank assembly are not serviceable. A similar vent for the fuel tank pressure sensor is also located in front of the fuel tank. A leak from this vent while the EVAP system is pressurized indicates the fuel tank pressure sensor is leaking.

Check for the following conditions:
^ A damaged, loose, missing, or incorrect fuel cap
^ A disconnected, damaged, pinched, or blocked EVAP purge line
^ A disconnected or damaged EVAP vent hose
^ An EVAP purge valve that is not opening
^ An EVAP vent valve that is not closing
^ A leaking fuel sender assembly O-ring
^ A leaking fuel tank or fuel filler neck

TEST DESCRIPTION

Steps 1 - 7:

Steps 8 - 14:

Steps 15 - 22:

The numbers below refer to the step numbers on the diagnostic table.
4. This step verifies that there is sufficient vacuum available for proper system operation.
5. This step is to determine if the loss of vacuum is due to the purge valve or the supply.
8. 20.37 mm Hg (10.86 in. H2O) is the maximum value displayed on the scan tool even though the actual pressure in the system may be higher.
17. Inspect the purge valve and lines for traces of carbon. Any carbon that is escaping from the canister may be preventing the valve from closing properly. If this condition is found, disconnect both ends of the purge line and blow out any contaminants by using the pressurized gas from the EVAP pressure/purge cart. Replace the purge valve and the canister/fuel tank.