Your 2021 Cadillac CT5 performs flawlessly under normal driving, but press the accelerator for passing power and the engine stumbles. Code P0302 confirms what you feel—cylinder 2 is misfiring, and it's happening specifically under load when demand is highest. This pattern provides important diagnostic clues.
Why Under Load Matters
Misfires that occur only under load—during acceleration, climbing hills, or high-speed cruising—indicate problems that marginal components can handle at idle but fail under stress:
- Higher cylinder pressures demand stronger spark
- Increased fuel demand challenges injectors
- Greater heat stresses ignition components
- Boost pressure (if turbocharged) increases demands
What P0302 Indicates
P0302 identifies cylinder 2 as the misfiring cylinder. On the CT5's engine, this gives you a specific cylinder to focus diagnostic efforts on, rather than chasing random misfires.
Common Causes of Load-Specific Misfires
Ignition Coil Weakness
An ignition coil may produce adequate spark at idle but fail to generate sufficient voltage under high cylinder pressure. Heat soak during hard driving exacerbates this.
Spark Plug Degradation
Worn electrode gap or carbon tracking creates spark that's fine at idle but insufficient for load conditions.
Fuel Injector Flow Issues
A partially clogged injector might deliver adequate fuel at idle but starve the cylinder under high demand.
Compression Problems
Low compression from worn rings or valves becomes more apparent under load when cylinder sealing is most critical.
Carbon Buildup
Carbon on intake valves (in direct injection engines) affects airflow more significantly under high-demand conditions.
Diagnostic Approach
- Swap test: Move cylinder 2's coil and plug to another cylinder. If the misfire follows, you've found the faulty component.
- Load test: Monitor misfire counts during acceleration on a dynamometer or controlled road test.
- Injector comparison: Test cylinder 2's injector flow rate against others.
- Compression test: Compare compression across all cylinders, especially under cranking conditions.
- Data analysis: Monitor misfire counters and fuel trim data during load.
Repair Options
- Ignition coil replacement: $150-$300
- Spark plug replacement: $150-$350
- Fuel injector: $200-$500
- Carbon cleaning (if applicable): $400-$700
- Compression-related repairs: $1,000+