EVAP system test description

• The EVAP system test finds gas leaks or blockage of EVAP system using the changes of the fuel tank pressure.
  • This test starts after sending an on-demand test signal 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 leak or blockage) 

• M-MDS send the stage 1 test start signal to the PCM.
• PCM controls the CV solenoid valve and purge solenoid valve to control the tank pressure to the targeted value.
• M-MDS detect the large leak or the purge line blockage if the tank pressure does not arrive at the target vacuum in specified period.
  Fig 1: Display Stage 1 Of EVAP System Test (Test For Large Leak Or Blockage)

  Courtesy of MAZDA MOTORS CORP.

Stage 2 test. (Test for small leak) 

• When fuel tank pressure arrived at the targeted pressure at stage 1 test, M-MDS sends the stage 2 test signal to the PCM to turn off the purge solenoid to keep the tank pressure.
• M-MDS detects the small leak if the tank pressure can not be kept within the target of specified period.
  Fig 2: Display Stage 2 Of EVAP System Test (Test For Small Leak)

  Courtesy of MAZDA MOTORS CORP.

Stage 3 test. (Test for blockage) 

• M-MDS sends the stage 3 test signal to the PCM to turn off the CV solenoid to check for blockage of EVAP system.
• M-MDS detects blockage of the CV solenoid valve or air filter if the tank pressure does not arrive at the target (atmosphere).
  Fig 3: Display Stage 3 Of EVAP System Test (Test For Blockage)

  Courtesy of MAZDA MOTORS CORP.