When your 2020 Chevrolet Colorado displays the P0305 code, the engine control module has detected repeated misfires in cylinder 5. The 2020 Colorado is available with the 2.5L four-cylinder, 3.6L V6, or 2.8L Duramax diesel. P0305 is valid on the V6 configuration but anomalous on the four-cylinder, which has only cylinders 1-4.
Identifying Your Colorado's Engine
Check your door jamb sticker or RPO codes to confirm which engine is installed. The base 2.5L I-4 produces 200 horsepower. The 3.6L V6 produces 308 horsepower and is the most popular option. The 2.8L Duramax diesel is an inline-four (P0305 anomalous). Only the V6 has a cylinder 5.
Cylinder 5 Location on 3.6L V6
On the 3.6L V6, cylinder 5 is located on the rear bank toward the firewall. GM's V6 configuration places cylinders 1, 3, and 5 on the rear bank and 2, 4, and 6 on the front bank. Access requires removing engine covers and possibly air intake components.
Common Causes on the V6
Spark plug wear is the primary cause, especially if approaching 100,000 miles. Ignition coil failure can occur at cylinder 5. Direct injection leads to carbon buildup on intake valves over time. Fuel injector issues can cause lean misfires. Vacuum leaks around the intake affect cylinder-specific air-fuel ratios.
Diagnostic Process
Confirm you have the V6 engine. Access cylinder 5's spark plug and inspect for wear or fouling. Test the ignition coil. Check for vacuum leaks. On higher-mileage trucks, intake valve carbon inspection may be beneficial.