EVAP system test description

The EVAP system test finds gas leaks in the system using the PCM to monitor changes in the air pump load current of the EVAP system leak detection pump. This test starts after sending an on-demand test signal from the WDS to the PCM. The PCM controls the air pump and change-over valve operation and also stores the load current of the air pump as follows:
1. The PCM commands turn the air pump on and retrieve the air pump load current value (LDP_MON PID) as a reference current (LDP_REF PID).
2. After retrieving a reference current value, the PCM commands the change-over valve to open, then captures the air pump load current value (LDP_MON PID) as idle current (LDP_IDL PID). The EVAP system will be pressurized from this phase.
3. The PCM continues to monitor the air pump load current value (LDP_MON PID) until the end of the test.
You can confirm whether any EVAP gas leak occurred or not by reading the test results.

Fig 1: EVAP System Test Signal Waveform
Courtesy of MAZDA MOTORS CORP.