Evaporative Emission (EVAP) Purge Flow System Monitor
The purpose of the EVAP purge flow system monitor is to verify the flow of fuel vapor from the EVAP canister purge valve to the engine. The electrical function of the Purge Flow (PF) sensor is initially checked before the flow test can begin. Inputs from the Intake Air Temp (IAT) sensor, Mass Air Flow (MAF) sensor and Vehicle Speed Sensor (VSS) are used to enable the flow test.
The flow test will detect a hose blockage or disconnection between the EVAP canister purge valve and the intake manifold. It will not detect a detached hose from either the valve to the EVAP canister or from the EVAP canister to the fuel tank.
The EVAP purge flow test will initiate when a 75% duty cycle is commanded on the EVAP canister purge valve during engine operation. At this time, the Purge Flow (PF) sensor will take a reading while fuel vapor is flowing to the engine. See Fig 1. The EVAP canister purge valve is then commanded closed (from 75% to 0% duty cycle). A second reading will be taken by the PF sensor after a calibrated time period of no fuel vapor flow to the engine. If the PF sensor does not react as expected to the sudden lack of fuel vapor flow to the engine, the PCM generates an EVAP canister purge valve fault DTC. If the difference between the two PF sensor readings taken (flow versus no flow) is not greater than a calibrated threshold, DTC P1443 (EVAP canister purge valve malfunction) will be set.
The Malfunction Indicator lamp (MIL) is turned on for DTCs P0433, P1443, P1444 and P1445 after two occurrences of the same fault.