The P0304 code in your 2020 Chevrolet Suburban indicates the engine management system has detected persistent misfires in cylinder 4. As the final year of the K2XX generation, this full-size SUV's V8 engine features Active Fuel Management—a cylinder deactivation system with specific diagnostic implications for misfire troubleshooting.
Understanding P0304 in the 2020 Suburban
The 2020 Suburban offers the 5.3L or 6.2L V8 engines, both featuring Active Fuel Management (AFM) cylinder deactivation. AFM shuts down four cylinders under light load using hydraulic switching lifters. Cylinder 4 is located on the right (passenger) bank toward the rear and is one of the AFM-controlled cylinders. This system has documented lifter concerns requiring diagnostic attention.
AFM System and Misfire Concerns
AFM's switching lifters have experienced documented failure patterns. Lifter collapse or sticking prevents proper valve operation, directly causing misfires. Warning signs include characteristic ticking noise at startup or idle. Standard misfire causes including spark plug wear and ignition coil degradation also apply. The combination requires systematic diagnosis.
Diagnostic Approach
Retrieve all codes including AFM-related faults. Listen for valve train noise suggesting lifter problems. Monitor cylinder activation status through scan tool data. Test ignition components—spark plug and coil condition. Verify oil level and quality as AFM operation depends on proper hydraulic pressure.
Repair Options
Replace ignition components showing wear. AFM lifter failure requires significant engine work for repair. Maintain proper oil change intervals with GM Dexos-approved oil. Consider AFM disabler devices to reduce lifter cycling wear on vehicles without existing lifter damage.