When your 2020 Chevrolet Suburban displays the P0305 code, the engine control module has detected repeated misfires in cylinder 5. The 2020 Suburban (final year of the eleventh generation) is powered by either the 5.3L V8 or 6.2L V8 engine, both of which have eight cylinders, making P0305 a legitimate diagnostic code.
2020 Suburban Powertrain
The 2020 Suburban offers the 5.3L EcoTec3 V8 (355 hp) as the standard engine and the 6.2L EcoTec3 V8 (420 hp) as an upgrade. Both engines feature Active Fuel Management (AFM) cylinder deactivation and direct fuel injection.
Cylinder 5 Location
On GM's V8 engines, cylinder 5 is at the front of the driver side (left) bank. GM's firing order places odd-numbered cylinders (1,3,5,7) on the driver side and even cylinders (2,4,6,8) on the passenger side.
Common Causes
AFM lifter failures are a known concern on GM V8 engines. The cylinder deactivation system uses special lifters that can collapse or fail, causing misfires in affected cylinders. Spark plug wear occurs over time, especially with towing. Ignition coil failure is possible. Carbon buildup from direct injection affects valve sealing.
Diagnostic Process
Read all codes including AFM-related codes. Inspect cylinder 5's spark plug for wear or fouling. Test the ignition coil. Check oil level and quality—AFM requires proper lubrication. If lifter failure is suspected, valve train inspection and compression testing may be necessary.