The 2021 MINI Cooper S and JCW equipped with the B48 2.0-liter turbocharged engine setting P0301 indicates a cylinder 1 misfire. This BMW-developed engine is shared across MINI and BMW models, providing well-documented service procedures.
B48 Engine Overview
The B48 is a 2.0-liter turbocharged four-cylinder producing 189-228 horsepower depending on MINI variant. It features direct injection, variable valve timing (Valvetronic), and twin-scroll turbocharging. Cylinder 1 sits at the front of the engine, closest to the timing chain.
Cylinder 1 Misfire Symptoms
A single-cylinder misfire produces rhythmic roughness at idle. The pattern is consistent because the same cylinder misfires each firing cycle. You may notice subtle vibration through the steering wheel or feel pulsing at idle. Under load, the sensation may diminish as other cylinders mask power loss.
Ignition Component Testing
The B48 uses individual coil-on-plug ignition. Swap the cylinder 1 coil with another cylinder—if the misfire moves, the coil failed. Spark plug inspection reveals combustion conditions through electrode wear, deposits, and coloring.
Fuel Injector Considerations
Direct injection operates at high pressure for precise fuel delivery. Injector issues include complete failure, restricted flow, or spray pattern problems. BMW/MINI diagnostic equipment performs injector balance testing to compare cylinder 1 against others.
Timing Chain Awareness
While B48 timing chains are generally reliable, cylinder 1's proximity to the timing system means any timing deviation affects it first. Unusual timing noises combined with cylinder 1 misfires warrant timing chain inspection.
Repair Costs
Ignition coil replacement costs $150-300 at MINI dealers. Spark plug service runs $200-350. Fuel injector replacement ranges $400-700 per injector. Carbon cleaning service costs $500-1,000.