P0312: Misfire detected on cylinder 12
Cylinder 12 misfire
Severity: Inspect soon
P0312 means the computer detected cylinder 12 not firing properly. The engine usually keeps running but rough, so get it checked soon to avoid damaging the catalytic converter.
It gets more serious if:
- Stop: The check engine light flashes while you drive. A flashing light means a misfire severe enough to overheat the catalytic converter, so ease off and stop driving as soon as it is safe.
P0312 in short
P0312 means the engine computer detected a misfire on cylinder 12, which is not firing as it should. The usual causes are that cylinder's spark plug, ignition coil, wiring or fuel injector. The engine usually runs but rough, so get it inspected soon and stop driving if the check engine light flashes.
The computer watches the crankshaft speed. When cylinder 12 fails to fire, the crankshaft slows slightly at that point, and the computer sets P0312.
TroubleCodes.net lists the cylinder 12 spark plug, coil, wiring and fuel injector as the common causes. Because the code names one cylinder, the fault is usually in that cylinder's own parts, not a system-wide fault.
Both the Delaware DMV list and TroubleCodes.net give the same meaning. This code applies to engines with 12 or more cylinders.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Worn or fouled cylinder 12 spark plug
Common general cause- Why it ranks here
- TroubleCodes.net lists the cylinder's spark plug first, and a plug is the cheapest and most common misfire part.
- What would change this
- Rises if the plug is worn, fouled or wet. Falls if it looks normal.
Cause 2: Failed cylinder 12 ignition coil or its wiring
Common general cause- Why it ranks here
- The coil and its wiring are listed with the plug as the ignition-side causes for this cylinder.
- What would change this
- Rises if the misfire follows the coil when it is swapped with a neighbour. Falls if it stays on the cylinder.
Cause 3: Cylinder 12 fuel injector not delivering fuel
Common general cause- Why it ranks here
- The injector is the fuel-side cause TroubleCodes.net lists for this cylinder.
- What would change this
- Rises if plug and coil are good and the injector circuit or spray test fails.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all stored codes and freeze-frame data, and note whether other cylinders also show misfires.
IfOnly cylinder 12 is stored
It meansLook at that cylinder's own plug, coil and injector.
IfSeveral cylinders or P0300 are stored
It meansThe cause may be shared, such as fuel or air, rather than one cylinder's parts.
Step 2: With the engine off and cool, swap the cylinder 12 coil with one from another cylinder, clear the codes and see which cylinder the misfire code names next.
Warning:Ignition coils carry very high voltage and the engine bay can be hot. Disconnect only with the engine off, and let a shop do it if unsure.
IfThe misfire moves with the coil
It meansThe coil is faulty.
IfThe misfire stays on the same cylinder
It meansCheck the plug and injector.
Step 3: Remove and inspect the cylinder 12 spark plug, and have the injector circuit tested.
Warning:Remove plugs only on a cold engine to avoid burns and thread damage, and work around fuel lines carefully.
IfThe plug is worn or fouled
It meansReplace the plug.
IfThe plug is fine
It meansTest the injector.
Symptoms
- Rough or shaking engine at idle
- Reduced power and worse fuel economy
- Flashing check engine light Gets more serious: stop and have it checked.
How to fix
On your vehicle
We don't have reviewed vehicle-specific evidence for P0312 yet. The causes and tests above apply across vehicles.
Related codes
Sources and review
- P0312 trouble code
- Diagnostic Trouble Code (DTC) list
- 2001 Lincoln Continental Owner's Guide - Warning lights (Check engine)
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error