P0302

P0302 means cylinder 2 specifically is misfiring per the crankshaft-deceleration monitor. The shop-floor diagnostic flow is identical to any cylinder-specific misfire: pull plug and coil from cylinder 2, read the plug (carbon-fouled, oil-wet, fuel-wet, or normal-but-dead), swap the coil with an adjacent cylinder, clear the code, and see if the misfire follows the coil. If swapping doesn't fix it, swap plugs. If swapping plugs doesn't fix it, run a compression test on cylinder 2 — anything below 85% of the highest-reading cylinder is a mechanical problem (rings, valve, head gasket between 2 and an adjacent cylinder). If compression is good, the next test is an injector balance/flow test: a clogged injector flows less fuel and creates a lean misfire that won't show up on a coil/plug swap. A 10-15 minute coil swap catches roughly 60% of P030X codes on vehicles with over 80,000 miles.

Vehicle-specific patterns: 2007-2012 Nissan Altima/Sentra with the QR25DE 2.5L frequently throws P0302 from a known timing-chain stretch issue that retards cam timing on the rear cylinders specifically — there's a Nissan TSB and extended warranty in some markets, check VIN coverage before quoting a coil pack. 2004-2008 Chrysler/Dodge 3.5L and 4.0L V6 (Pacifica, 300, Charger) commonly throws P0302 from a cracked rear exhaust manifold causing post-cat O2 confusion and a lean misfire on cylinder 2. 2010-2015 Hyundai Sonata/Tucson with the Theta II 2.4L GDI frequently throws P0302 from carbon buildup on the direct-injection intake valves (no port-injection wash); walnut blast resolves it. Estimated repair: $40 (single coil DIY) to $2,500+ (timing chain job on the Nissan QR25).