Intake or Purge Issue for Buick

This bulletin applies to 2012-2019 Buick Enclave vehicles equipped with a 3.6L engine. The service engine soon (SES) light may be on, accompanied by diagnostic trouble code (DTC) P0171 and/or P0174 in the engine control module (ECM). This indicates a possible vacuum leak in the intake or purge system.

1. Warm the engine to operating temperature, and monitor/record long-term and short-term fuel trims. Plug both the manifold hole and the disconnected foul air tube hole.

2. Shut the engine off and disconnect the foul air tube from the intake manifold. Detach the foul air tube and plug both sides.

3. Restart the engine and monitor long and short fuel trims. If both the previously recorded fuel trims were at a positive value above five and now the short trim has gone to a consistent negative value during this test, replace the foul air tube. If the previously recorded short trim is at a value above  5 and the long fuel trim is between negative-2 and 2, but during the test the short trim has gone to zero or negative value, replace the foul air tube.

4. If the fuel trims in steps 1 or 2 did not change, proceed with a purge valve test.

5. If during the test the fuel trims did not change after the foul air tube was capped off, shut the engine off and ensure that the foul air tube and manifold plugs have been removed and re-install the foul air tube to the manifold. Locate the purge valve on the intake manifold. Disconnect the vacuum hose and power supply from the purge valve. Restart the engine and place your finger or a vacuum gauge over the open port on the purge valve.

6. If you feel vacuum or read vacuum on the gauge at the port of the valve, it will need to be replaced. Shut the engine off and reinstall detached components. If no vacuum is felt or measured at the purge valve port, refer to the DTC in the service manual for further diagnosis.