EVAP system test description

• The EVAP system test finds gas leaks or blockage in the EVAP system using changes in the fuel tank pressure.
  • This test starts after an on-demand test signal is sent from the M-MDS to the PCM.
  • This test consists of three stages, and each stage is performed automatically as follows:

Stage 1 test (Test for large leaks or blockage)

• The M-MDS sends the stage 1 test start signal to the PCM.

Fig 1: EVAP System Test (Stage 1)

Courtesy of MAZDA MOTORS CORP.

• The PCM controls the CV solenoid valve and the purge solenoid valve to control the fuel tank pressure to the targeted value.
• The M-MDS detects large leaks or purge line blockage if the fuel tank pressure does not arrive at the target vacuum in a specified period of time.

  Stage 2 test (Test for small leaks)

• When the fuel tank pressure reaches the targeted pressure during the stage 1 test, the M-MDS sends the stage 2 test signal to the PCM to turn off the purge solenoid valve and maintain the fuel tank pressure.

Fig 2: EVAP System Test (Stage 2)

Courtesy of MAZDA MOTORS CORP.

• The M-MDS detects a small leak if the fuel tank pressure cannot be maintained within the target for the specified period of time.

  Stage 3 test (Test for blockage)

• The M-MDS sends the stage 3 test signal to the PCM to turn off the CV solenoid valve and check for blockage in the EVAP system.

Fig 3: EVAP System Test (Stage 3)

Courtesy of MAZDA MOTORS CORP.

• The M-MDS detects blockage in the CV solenoid valve or air filter if the fuel tank pressure does not reach the target (atmosphere).