EVAP system leak inspection using the M-MDS: Notes

EVAP system test outline

The EVAP system test, which can be substituted for the run drive cycle as an EVAP control system repair confirmation method, can detect the small/large leak or blockage without run-drive cycle.

NOTE:

The M-MDS cannot detect "very small leaks". To identify the leak point, use the leak tester or ultrasonic leak detector.
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 Description (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 Description (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 Description (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).