A P0303 diagnostic code in your 2020 Chevrolet Suburban indicates cylinder 3 is experiencing misfires that the engine control module has identified as exceeding acceptable limits. The 2020 Suburban, representing the final year of the GMT K2UC generation, offers the 5.3L EcoTec3 V8 and the more powerful 6.2L EcoTec3 V8. Both engines utilize Active Fuel Management (AFM) cylinder deactivation technology.
Cylinder 3 Position in Suburban V8s
Both Suburban V8 engines use GM's traditional cylinder numbering with cylinder 3 on the driver's side (left bank), second position from the front. This location provides reasonable access for spark plug and coil service, though the large SUV's engine bay requires some reaching.
Active Fuel Management Considerations
The 5.3L and 6.2L engines feature AFM, which deactivates cylinders 1, 4, 6, and 7 during light-load cruising. While cylinder 3 isn't a designated deactivation cylinder, AFM system issues affecting oil pressure delivery or control solenoids can impact overall engine operation. Additionally, the hydraulic lifters throughout the engine can develop problems.
Common P0303 Causes
At approximately four to five years of age, the 2020 Suburban may experience various misfire causes. Spark plug degradation is common depending on mileage and driving conditions. Ignition coil failures occur from heat cycling over time. Fuel injector issues—either deposits or electrical failure—affect fuel delivery. Carbon buildup in these direct-injected engines accumulates over miles driven.
Mechanical Possibilities
More serious causes include AFM lifter failure (though primarily affecting deactivation cylinders), valve seat recession, and head gasket issues. These typically produce additional symptoms like oil consumption, unusual noises, or coolant loss.