Mechanical System Testing

WARNING: This page is about a different car, the 2009 GMC Sierra and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description .
Ignition ON, verify the scan tool hood position parameter displays Open.
- If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.
Connect a vacuum gage to the EVAP vacuum tube fitting on the electronic throttle body. DO NOT use a compound pressure and vacuum gage. The vacuum gage on a hand held vacuum pump will work fine for this test.
Start the engine. Allow the engine to reach normal operation temperature.
With a scan tool, command each VLOM solenoid ON, one at a time. Each time a solenoid is command ON, you should observe a fluctuating drop of intake manifold vacuum, and a misfire on the cylinder that was deactivated.
- If there is no fluctuating drop in engine vacuum, or the engine does not misfire, then refer to Cylinder Deactivation (Active Fuel Management) System Diagnosis .