A check engine light accompanied by engine vibration and P0302 code in your 2018 GMC Acadia indicates cylinder 2 is misfiring, disrupting the V6's smooth operation. Whether equipped with the 2.5L four-cylinder or 3.6L V6, consistent misfires require diagnosis to prevent catalytic converter damage.
Engine Options
The 2018 Acadia offers the 2.5L four-cylinder or 3.6L V6. Cylinder 2 location and diagnostic approach differ between these engines. The V6 is more common in this model and uses coil-on-plug ignition that's prone to individual coil failures.
Why Vibration Occurs
When cylinder 2 fails to contribute power consistently, the engine runs unevenly. The vibration results from unbalanced forces as other cylinders compensate for the misfiring cylinder. This is most noticeable at idle when there's no other motion to mask it.
Common Causes
The 3.6L V6's ignition coils commonly fail one at a time. Spark plug wear, particularly after extended intervals, causes misfires. Fuel injector problems specific to cylinder 2 affect combustion. Carbon buildup from direct injection reduces airflow. Less commonly, valve or compression issues cause persistent misfires.
Diagnostic Priority
Start with the most common and accessible components: spark plug and ignition coil inspection. These fail most frequently and are easiest to diagnose through visual inspection and component swapping.