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EVAP Service Bay Test

The EVAP service bay test is designed to enable the PCM to run the on-board EVAP system diagnostic. If the diagnostic detects any system leaks or component failures the PCM stores the appropriate DTC under Last Test Failed. Throughout the diagnostic test sequence the PCM uses the fuel tank pressure (FTP) sensor in order to monitor the vapor pressure in EVAP system. Unexpected changes in EVAP system pressure can indicate the incorrect operation of EVAP system components and detect system leaks.

The EVAP service bay test is an automated sequence of four individual EVAP test events. The following table provides an overview of each event:

Automated EVAP Service Bay Test Sequence

Diagnostic Test Event EVAP Purge Solenoid EVAP Vent Solenoid EVAP Vacuum Leak Pump FTP Sensor Pressure, mm Hg (in H2O)
First Event OFF, CLOSED OFF, OPEN OFF for 10 Seconds, then ON for 30 seconds Zero, then decreasing, negative pressure
Second Event OFF, CLOSED ON, CLOSED ON Sudden pressure increase
Third Event OFF, CLOSED ON, CLOSED ON Pressure decreases to lower limit and then stabilizes, vacuum decay test
Fourth Event ON, OPEN ON, CLOSED ON Pressure returns to zero in less than 10 seconds

The EVAP service bay test can require up to 15 minutes in order to run. If the test detects a fault in the first or second event, the test will end in less than 2 minutes. When the service bay test is complete, the EVAP I/M System Status updates to YES. In order to perform the EVAP service bay test with the scan tool follow the procedures below:

IMPORTANT: Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. Fuel tank pressure may increase on a hot vehicle due to the thermal expansion of vapors in the fuel tank. Perform the EVAP service bay test when the temperature of the fuel is less than 35°C (95°F).
IMPORTANT: Fuel tank fill levels can affect the results of the diagnostic procedure. The fuel level in the fuel tank should be between 25-75 percent of full.
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Ensure that the fuel filler cap is installed securely.
  4. Perform the scan tool Clear DTC function.
  5. Enable the EVAP Service Bay Test with the scan tool.
  6. If the scan tool displays Test in Progress, the service bay test is enabled.
  7. If the scan tool displays Test Failed, the test was not enabled. Exit the test screen on the scan tool and turn OFF the ignition for 30 seconds. After 30 seconds turn ON the ignition and enable the test again with the scan tool.
  8. DO NOT turn OFF the ignition or select EXIT on the scan tool during the Test in Progress display.
  9. WAIT until the scan tool displays Test Complete.
  10. Check for DTCs under Last Test Failed with the scan tool.
  11. No DTCs stored indicates that the EVAP system diagnostic has passed and no EVAP system faults are present.
  12. Any stored DTC indicates that an EVAP system fault exists. Go to the appropriate DTC table and perform the diagnostic procedure as necessary.
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