Important: Proper oil viscosity is critical to Cylinder Deactivation (AFM) Operation. ALWAYS verify proper engine oil viscosity and oil change interval BEFORE beginning AFM system diagnosis. Improper viscosity or excessively dirty engine oil may cause improper operation. Under NO circumstances should engine oil additives be used, unless recommended by General Motors. If you suspect the engine oil is dirty, contaminated, or of improper viscosity, change engine oil and filter prior to performing any Cylinder Deactivation diagnostics. If it is found that one or more of the Active Fuel Management (AFM) lifters are not operating properly and needs replacing, replace all 6 AFM lifters and the lifter guide as an assembly.

1. Check the engine oil level. Fill as required.
2. Using the scan tool, check for diagnostic codes within the powertrain control module (PCM). Refer to Diagnostic System Check - Vehicle. Repair as required.
3. Verify proper engine oil pressure. Refer to Engine Mechanical Specifications.
4. Verify proper operation of the Cylinder Deactivation (AFM) system components. Refer to Cylinder Deactivation (Active Fuel Management) Valve Lifter Oil Manifold Diagnosis and Testing.
5. Replace all Cylinder Deactivation (AFM) valve lifters as an assembly. Refer to Valve Lifter Replacement.