P0455

Diagram Chart:

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

^ The following DTCs not set: P0100, P0115, P0116, P0120, P0130 thru P0161, P0300 thru P0306, P0443, P0446, P0450, P0501, P0505, P0560

^ The Vehicle Speed is 0 mph.

^ The engine is at idle

^ The ECT at start is between -8°C (17°F) and 100°C (212°F).

^ The Closed Loop is enabled.

^ The fuel tank pressure is less than 10.12 kPa (4 in. H2O).

^ The Engine Load less than 2.7 milliseconds.

^ The IAT is greater than -8°C (17°F).

^ The MAF less than 7.5 g/s

^ The System Voltage is above 11 volts

^ The Engine Run Time is at least 16 minutes 25 seconds.

^ The AIR system is inactive.

^ The AIR system diagnostic is not running.

^ The Short Term Fuel Trim at the beginning of the test is greater than -5%.

CONDITIONS FOR SETTING THE DTC

The diagnostic test has run to completion and determined that this DTC was detected.

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 does not fail.

^ A History DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other emission related diagnostic.

^ The ECM battery voltage is interrupted.

^ The scan tool clears the MIL/DTC.

DIAGNOSTIC AIDS

Check for the following conditions:

^ A missing or damaged fuel cap

^ A disconnected, damaged, pinched, or blocked EVAP purge line

^ A disconnected or damaged EVAP vent hose

^ A disconnected, damaged, pinched, or blocked fuel tank vapor line

^ An EVAP canister purge valve problem (non-electrical)

^ An EVAP vent solenoid problem (non-electrical)

^ A damaged EVAP canister

^ A leaking fuel sender assembly O-ring

^ A leaking fuel tank or fuel filler neck

If no apparent cause of a large leak can be found, the vehicle may have been left running during refueling. By coincidence, the proper conditions may have been met in order to run the diagnostic during the time the fuel cap was off or loose.

TEST DESCRIPTION

The number(s) below refer to the step number(s) on the Diagnostic Table.

4. This step verifies that there is sufficient vacuum available at the Purge valve for proper system operation.

5. Verifies that the fuel tank vacuum sensor re-zeros to ambient pressure.

6. Determines whether or not the EVAP system is sealed sufficiently to be pressurized. If not, a large leak must be located and corrected.

7. 11.8 in. H2O is the maximum value displayable on the scan tool even though the actual pressure is higher. This step verifies that vapor flow is not blocked somewhere between the service port and the fuel tank.

10. In the previous step, a leak was detected. This step separates the front half of the system (canister to engine) from the rear half of the system (canister to fuel tank), in order to narrow down the location of the leak.

17. Inspect the Purge valve and vacuum 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.