Evaporative Emission Vapor Management Flow System Monitor

Vapor Management Flow System Monitor:

The EVAP Vapor Management Flow System Monitor is designed to verify that the EVAP canister purge valve is functioning properly and to verify the flow of fuel vapor from the EVAP canister purge valve to the engine. The electrical function of the EVAP canister purge valve is initially checked before the flow test can begin. Inputs from the ECT sensor, IAT sensor, MAF sensor and VSS are used to enable the flow test.

NOTE: The EVAP vapor management flow test will not run if a EVAP canister purge valve malfunction is indicated. The Diagnostic Trouble Code (DTC) associated with an electrical fault of the EVAP canister purge valve is P0443 (EVAP system control valve circuit malfunction).

Before the flow test is performed, the PCM will calculate how much fuel vapor is present while purging under engine operation. If the amount of fuel vapor calculated is above a calibrated threshold, the PCM assumes that there must be fuel vapor flow to the engine and that the EVAP canister purge valve is functioning properly. If this condition exists, the idle speed portion of the EVAP vapor management flow test will be bypassed and the test will pass and complete.

If the amount of fuel vapor calculated is below a calibrated threshold, the idle speed portion of the EVAP vapor management flow test must be executed to verify that the EVAP canister purge valve is functioning properly. An assumption of the flow test is that regardless of the fuel vapor in the EVAP canister, some portion of the fuel vapor flow will be air. The flow test will calculate the increase in the idle air requested by the PCM when the duty cycle on the EVAP canister purge valve is reduced from 75% to 0%.

If the calculated increase in air flow exceeds a calibrated threshold, the PCM assumes the EVAP canister purge valve is functioning properly. If the calculated increase in air flow is negligible, the EVAP canister purge valve is not functioning properly. The DTC associated with this condition is P1443 (EVAP control system purge control valve malfunction).

The Malfunction Indicator Lamp (MIL) is activated for DTCs P0443 and P1443 after two occurrences of the same fault.