Vacuum Leak for Chevy

This bulletin applies to 2012-2019 Chevy Traverse, 2015-2016 Colorado, 2015-2017 Equinox and 2015-2019 Impala vehicles. The SES light may be on accompanied by DTC P0171 and/or P0174 stored in the ECM. The likely cause is a vacuum leak in the intake or purge.

Operate the engine at normal temperature and monitor/record long term and short term fuel trims. Plug both the manifold hole and the disconnected  foul air tube hole. Shut the engine off and disconnect the foul air tube from the intake manifold.

Detach the foul air tube from the connection shown in the following photo (see red arrow) and plug both sides. Restart the engine and monitor long and short fuel trims. If both the previously recorded long and short fuel trims were at a positive value above 5 and now the short term has gone to a consistent negative value during this test, replace the foul air tube. If the previous short trim is above positive 5 and the long trim is between -2 and +2, but during the test the short trim has gone to a zero or negative value, replace the foul air tube. If the fuel trims in the previous steps did not change, proceed to a purge valve test. Only replace the manifold if the afore-noted test impacted fuel trims.

Shut off the vehicle and ensure that the foul air tube and manifold plugs have been removed, and reinstall 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. If you feel vacuum or read vacuum on the gauge, the valve must be replaced.