EVAP system leak inspection using the M-MDS

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 Chart - Stage 1 Test
    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 Chart - Stage 2 Test
    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 Chart - Stage 3 Test
    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).
EVAP system malfunction determination
The M-MDS detects small/large leaks or blockage based on the fuel tank pressure at the end of the EVAP test.

The target vacuum was not obtained during the EVAP test. A large leak or blockage is suspect.

This result means the fuel tank pressure did not reach the target pressure during the stage 1 test.
- Inspect for large leakage or inspect the purge solenoid valve operation and related hoses.
- Repair or replace any malfunctioning parts.

The target vacuum was not maintained during the EVAP test. A small leak is suspect.

This result means the fuel tank pressure was not maintained at the target pressure during the stage 2 test,
- Run the EVAP test again after retightening the fuel filler cap.
- If a small leak is suspected again, use the leak tester or ultrasonic leak detector to identify the leak point.
- Repair or replace any malfunctioning parts.

Blockage in EVAP system.

This result means the fuel tank pressure did not return to atmosphere during the stage 3 test.
- Inspect the CV solenoid, air filter, charcoal canister and related hoses for blockage.

No large leaks or blockage were detected in the EVAP system.

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

A small leak in the purge solenoid valve is suspect.

This result means the fuel tank pressure decreases to the minus side during the stage 2 test.
- Inspect the purge solenoid valve. Refer to the article.

Evaporative system test procedure

Verify that all PIDs are within the following specifications.

Specification

PID	PID Range
BARO	74.9 kPa {0.764 kgf/cm² , 10.9 psi} or more
FLI	15-85%
ECT	ECT minus IAT -10-25 °C {-18-45 °F}
IAT	ECT minus IAT -10-25 °C {-18-45 °F}

NOTE:

To successfully perform this procedure, all PIDs must be within specifications before proceeding to the next step.

Select the following items from the initialization screen of the M-MDS.
- Select "Powertrain".
- Select "Fuel".
- Select "EVAP Test".
  - Verify that the ECT and IAT are within specifications on the confirmation screen. To successfully perform this procedure, the ECT and IAT must be within the specification before proceeding to the next step.
  - The fuel Level must be maintained within 15 %-85 % . The PCM will cancel the EVAP test if the fuel level is lower than 15 % or higher than 85 % .
Verify the test results described on the M-MDS and follow the instructions.