Evaporative Emissions System: Description and Operation

EVAP Leak Check System Description

ECM boots up EVAP leak check system 5 hours after changing ignition mode of keyless push start system to "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 detection pump (4) and reference orifice (5).

ECM (17) executes EVAP system monitoring according to the following steps.

NOTE:

During EVAP leak check, operation noise may be heard from some components (motor or pump) for several minutes. This sound is normal and does not indicate a malfunction.

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

If the EVAP system minimum pressure is higher than the reference pressure, it means 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.

When filling up the vehicle with fuel during EVAP system monitoring, ECM stops EVAP system monitoring.

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