P0312 Cylinder 12 Misfire Detected

P0312 points to a misfire detected on cylinder 12. The controller detects uneven crankshaft speed contribution from cylinder 12.

Code details

Generic OBD-II · P0

System: Ignition / Misfire
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace cylinder 12 parts before separating ignition, injector, compression, and air-leak causes.

Symptoms of P0312

Rough idle, shaking, or a stumble under acceleration.
A flashing check-engine light during an active misfire.
Power loss and higher fuel consumption.

Common causes of P0312

Worn spark plugs, ignition coils, or plug wires.
Fuel-delivery problems — injectors, pressure, or a lean/rich mixture.
Vacuum leaks, low compression, or a mechanical fault in that cylinder.

Useful checks before replacing parts

Review cylinder 12 misfire counters, freeze-frame load, fuel trims, injector command, ignition data, and compression or leakdown results.
Inspect ignition or glow components, injector wiring and flow, harness heat damage, vacuum leaks, compression, and fuel quality.
Determine whether the misfire is idle-only, load-dependent, cold-only, hot-only, or paired with cylinder 12 injector codes.

Related OBD-II codes

These nearby ignition / misfire entries can help compare wording and pin down the fault area.