The P0303 diagnostic trouble code on your 2024 GMC Sierra indicates the engine control module has detected consistent misfires in cylinder 3. The Sierra offers multiple V8 engine options, each with specific characteristics affecting misfire diagnosis.
Engine Options and Cylinder 3 Location
The 2024 Sierra is available with the 5.3L L84 V8, 6.2L L87 V8, or the 3.0L Duramax diesel. On the V8 engines, cylinder 3 is located on the driver's side bank. Both V8s feature Dynamic Fuel Management (DFM), which can complicate misfire diagnosis due to cylinder deactivation.
Common Causes
- DFM Lifter Problems: Cylinder deactivation lifters can fail, causing misfires
- Ignition Coil Failure: Individual coil packs fail over time
- Spark Plug Issues: AFM/DFM engines have specific plug requirements
- Fuel Injector Problems: Direct injection systems can develop deposits
- Valve Train Concerns: Lifter tick and failure are known issues
Diagnostic Approach
Connect a GM-compatible scanner to access DFM-specific data. Monitor if misfires correlate with cylinder deactivation events. Test ignition components systematically. Check for GM technical service bulletins related to AFM/DFM lifter issues.
Repair Solutions
Replace failed ignition coils with AC Delco components. Install spark plugs meeting GM specifications for DFM engines. For lifter-related misfires, GM has issued service procedures for AFM/DFM lifter replacement. Update ECM software if applicable TSBs exist.