Evaporative Emissions System: Description and Operation

EVAP Leak Check System Description




ECM boots up EVAP leak check system after 5 hours from ignition switch off and ECM starts EVAP leak monitoring by operating EVAP leak check module (1).

EVAP leak check module consists of EVAP leak check pressure sensor (2), EVAP canister vent valve (3), EVAP leak detecting pump (4) and reference orifice (5).

ECM (17) executes EVAP system monitoring by the following step.
1. ECM measures EVAP system initial pressure (P1) by EVAP leak check pressure sensor while EVAP canister vent valve is opened (OFF) and EVAP leak detecting pump is not operated (OFF).
2. ECM measures vacuum as reference pressure (P2) which is generated by getting suction air of EVAP leak detecting pump through reference orifice (equivalent of 0.5 mm (0.02 in.) diameter hole) while EVAP canister vent valve opened (OFF) [A] and EVAP leak detecting pump operated (ON).
3. ECM measures tank pressure as EVAP system maximum pressure (P3) when EVAP canister vent valve is closed (ON) [B] with EVAP leak detecting pump operated.
4. ECM measures vacuum as EVAP system minimum pressure (P4) while EVAP canister vent valve is closed (ON) with EVAP leak detecting pump operated.
5. ECM compares reference pressure to minimum pressure in EVAP system.

If the EVAP system minimum pressure is higher than the reference pressure, the system contains a leak which is greater than or equal to a leak caused by a 0.5 mm (0.02 in.) diameter orifice.

If the fuel is charged to vehicle during EVAP system monitoring, ECM stops EVAP system monitoring.

If ECM detects EVAP leak check module malfunction, ECM stops EVAP system monitoring and store the applicable DTC. When starting the engine after detecting the DTC, ECM turns on the MIL.