The P0303 diagnostic trouble code on your 2021 GMC Yukon indicates the engine control module has detected repeated misfires in cylinder 3. As the first year of the redesigned Yukon, the 2021 model introduced GM's T1 platform with advanced V8 engines.
V8 Engine Options
The 2021 Yukon offers the 5.3L L84 V8 or 6.2L L87 V8, both featuring Dynamic Fuel Management (DFM) for cylinder deactivation. Cylinder 3 is located on the driver's side bank. The 3.0L Duramax diesel is also available but has different diagnostic considerations.
Common Causes
- DFM Lifter Problems: Cylinder deactivation lifters can fail even on newer vehicles
- Ignition Coil Failure: Individual coil packs can develop issues
- Spark Plug Concerns: DFM engines require properly specified plugs
- Fuel Injector Issues: Direct injection system problems
- Software Calibration: First model year may have ECM updates available
Diagnostic Approach
Use GM's diagnostic tools to monitor DFM operation and misfire data. Check if misfires correlate with cylinder deactivation events. Research current TSBs for the T1 platform. Test ignition components systematically.
Repair Solutions
Replace faulty ignition coils with AC Delco parts. Install GM-specified spark plugs. For DFM-related issues, lifter replacement following GM procedures may be required. Check for and apply ECM software updates.