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Tricky Vacuum

This bulletin applies to 2012/2013 Buick Regal vehicles with the MIL on and with DTC P0442 set as current or in history (EVAP system small leak canister vent solenoid valve not sealing under vacuum).

During the EVAP system test for P0442, the EVAP Vent Solenoid (CVS) valve will be in a vacuum condition. During normal diagnostics, the system is pressurized to no more than 13 inches (0.5 psi), so a leak under vacuum may not be detected. It is possible for the CVS to seal when pressurized but may leak under vacuum. This leak may be intermittent as the seal may rotate when the CVS is cycled. This leak may also only be present in colder ambient temperature.

Do not replace the EVAP canister assembly for this concern unless it fails the leak test. The difficulty to determining the cause of the EVAP leak results in improper repairs and potential comebacks. If no leak is found after following system testing instructions in the service manual, follow these additional steps:

1. Connect the scan tool to the vehicle and command the EVAP system (vent solenoid valve) closed.

2. Start the engine and monitor the fuel tank pressure sensor output value for approximately two minutes.

3. Open the purge valve by commanding some percentage of purge.

4. Ensure that the canister vent solenoid is closed and monitor the FTP sensor for a vacuum to develop (purge & seal).

5. If vacuum does not develop, refer to purge valve diagnostics.

6. If vacuum does develop, command the EVAP system closed (purge & seal) and monitor for vacuum decay.

7. If a significant leakdown is not found, cycle the CVS and retest.

8. If a significant leakdown rate is found, replace the CVS with P/N 22740537.

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