System Inspection

Evaporative (EVAP) Emissions System Diagnostic Tests
The control module performs diagnostic tests in order to monitor the performance of the Evaporative (EVAP) emissions system. These test are as follows:

Excess Vacuum Tests
The control module monitors the fuel tank pressure sensor signal during the normal purging of the EVAP canister under various driving conditions in order to detect a malfunction in the fuel tank vent control components. If the Excess Vacuum tests run and pass the Purge Valve Leak Test will run. If the Excess Vacuum tests run and fail, a DTC P0446 is set.

Loaded Canister Test
The control module monitors the oxygen sensors during normal EVAP purging in order to determine if the EVAP canister is storing a sufficient amount of fuel vapors. If the test indicates that the EVAP canister is storing a sufficient amount of fuel vapors the remaining diagnostic tests for the EVAP system will store a pass. If the Loaded Canister Test indicates to the control module that an insufficient amount of fuel vapors are being stored by the EVAP canister, the Weak Vacuum Tests will run.

Weak Vacuum Tests
The Weak Vacuum Test is performed by the control module in order to determine if the EVAP control system is capable of achieving a sufficient vacuum in the system. During the normal purging of the EVAP control system the control module will perform the following:
- Command the EVAP vent valve ON (closed)
- Monitor the fuel tank pressure sensor signal

If the control module determines that sufficient vacuum is not achieved the control module will perform the following:
- Store a DTC P0440 after the first failed test
- Store the data in the Freeze Frame/Failure Records
- Turn the MIL ON after a second consecutive failed test

If the control module determines that sufficient vacuum is achieved the control module will perform the following:
- While the EVAP vent valve is ON (closed), turn the EVAP purge solenoid OFF (closed) and Run the Small EVAP Leak Test.
- Run the Purge Solenoid Leak Test, if the first Weak Vacuum Test passes.
- Turn OFF the MIL, if the MIL is ON because of a previous failed Weak Vacuum Test.
- Clear the data stored in the Freeze Frame for the DTC P0440.

The Weak Vacuum Tests will not run unless the Loaded Canister Test has run and failed.

Small EVAP Leak Test
The control module performs the Small EVAP Leak Test in order to detect a small leak in the following components of the EVAP system:
- The fuel tank
- The fuel filler cap
- The fuel filler neck
- The EVAP canister
- The EVAP vent valve
- The EVAP vapor pipes and hoses

The Small EVAP Leak Test does not test the EVAP purge solenoid for leaks.

In order to run the Small EVAP Leak Test the control module performs the following:
- Turn OFF the EVAP purge valve (closed).
- Following the passed Weak Vacuum Test and while the EVAP vent valve is still turned ON (closed), run the Small EVAP Leak Test.
- Monitor the fuel tank pressure sensor signal.

The control module monitors the vacuum trapped in the system. If the control module detects a excessive decrease in the vacuum that is trapped in the system a DTC P0442 is set.

Purge Valve Leak test
The control module monitors the fuel tank pressure sensor signal during a cold start in order to test the EVAP purge valve. With the purge valve OFF (closed) the VCM expects to detect no vacuum in the system. If the control module detects a vacuum while the Purge Valve Leak Test is being performed a DTC PI441 is set.