P0312 indicates that the engine control module has detected a misfire in cylinder 12. The code is set when crankshaft position sensor data or other monitoring inputs show irregular combustion events for that specific cylinder.
A worn or fouled spark plug or a failed ignition coil is the most common cause of a single‑cylinder misfire.
A clogged, leaking, or electrically defective injector can prevent proper fuel delivery to the cylinder.
An intake manifold or hose leak affecting only the runner for cylinder 12 can create a lean condition and misfire.
Worn piston rings, damaged valves, or a blown head gasket can reduce compression enough to cause a misfire.
Corroded, loose, or damaged wires and connectors can interrupt the signal to the coil or injector.
A control module failure is rare; it should be considered only after all other cylinder‑specific components have been verified.
In most cases the PCM is not the cause; the code is usually due to ignition, fuel, or mechanical issues in cylinder 12.
Continued misfire can damage the catalytic converter and increase emissions, so it should be addressed promptly.
Yes, the spark plug and ignition coil are the most common causes and are inexpensive to test or replace.
Driving with a persistent misfire can cause further damage; the vehicle should be diagnosed and repaired as soon as practical.