Damaged, worn or contaminated spark plug, or a faulty spark plug wire. Faulty ignition coil (coil pack). Faulty fuel injector. Fuel supply problems: fuel pump failure, running out of fuel, or fuel that doesn't meet the manufacturer's requirements. Vacuum leak or exhaust leak (listed by RepairPal). Engine sensor failure (listed by RepairPal). Poor compression, a burned exhaust valve or other internal engine failure. Faulty oxygen sensor(s) or catalytic converter (listed by OBD-Codes.com only). Defective engine computer, or PCM software that needs an update.

Replace the spark plug, plug wire or ignition coil on cylinder 12 (RepairPal lists ignition coil replacement as a common repair). Replace a faulty fuel injector once testing confirms it (RepairPal lists fuel injector replacement as a common repair). Repair vacuum or exhaust leaks, or fuel pump problems. Update the PCM software if the manufacturer has released an update. Repair mechanical problems such as a burned valve or low compression found by testing. Replace a failed catalytic converter.

P0312⚡ Ignition / engine misfireStop and fix promptly

P0312: Cylinder 12 Misfire Detected (Meaning, Causes, Fixes)

Q: What does P0312 mean?

P0312 means the engine computer has detected that cylinder 12 isn't firing properly, or in RepairPal's words, isn't sufficiently contributing to keeping the engine running. Spark plugs, plug wires and ignition coils are the usual suspects, but fuel injectors, fuel supply, vacuum or exhaust leaks, low compression and engine sensors can also set it. P0312 is a generic OBD-II code, so it applies to all OBD-II vehicles, though the repair steps vary by make and model. RepairPal explains that the engine control module (PCM) sets P0312 when it detects that cylinder 12 is not sufficiently contributing to keeping the engine running properly. A cylinder 12 only exists on engines with twelve or more cylinders, so this code is far rarer than P0301 to P0306, and cylinder numbering differs between engines, so check your service information to find which one is number 12. The sources list somewhat different causes. Both name spark plugs, ignition coils, fuel injectors, poor compression or internal engine problems, and a faulty computer or outdated PCM software. OBD-Codes.com also lists faulty oxygen sensors, a faulty catalytic converter, a burned exhaust valve and running out of fuel, while RepairPal adds engine sensor failure, exhaust and vacuum leaks, fuel pump failure and fuel that doesn't meet the manufacturer's requirements. Neither source gives a repair cost for this code.

Q: Can I keep driving with P0312?

Stop and fix promptly. RepairPal rates P0312 'Urgent', meaning a malfunction that can cause severe damage to the vehicle or harm the driver and passengers. OBD-Codes.com doesn't give it a severity rating, but notes the engine may stumble, hesitate or be harder to start. A misfire can damage the catalytic converter, so if the check engine light is flashing, ease off, avoid hard acceleration and get it checked as soon as you safely can.

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0312 means

P0312 is a generic OBD-II code, so it applies to all OBD-II vehicles, though the repair steps vary by make and model. RepairPal explains that the engine control module (PCM) sets P0312 when it detects that cylinder 12 is not sufficiently contributing to keeping the engine running properly. A cylinder 12 only exists on engines with twelve or more cylinders, so this code is far rarer than P0301 to P0306, and cylinder numbering differs between engines, so check your service information to find which one is number 12. The sources list somewhat different causes. Both name spark plugs, ignition coils, fuel injectors, poor compression or internal engine problems, and a faulty computer or outdated PCM software. OBD-Codes.com also lists faulty oxygen sensors, a faulty catalytic converter, a burned exhaust valve and running out of fuel, while RepairPal adds engine sensor failure, exhaust and vacuum leaks, fuel pump failure and fuel that doesn't meet the manufacturer's requirements. Neither source gives a repair cost for this code.

Severity: can I keep driving?

Stop and fix promptly

RepairPal rates P0312 'Urgent', meaning a malfunction that can cause severe damage to the vehicle or harm the driver and passengers. OBD-Codes.com doesn't give it a severity rating, but notes the engine may stumble, hesitate or be harder to start. A misfire can damage the catalytic converter, so if the check engine light is flashing, ease off, avoid hard acceleration and get it checked as soon as you safely can.

Common symptoms

Check engine light on, or flashing while the misfire is happening
Engine stumbles or hesitates (listed by OBD-Codes.com)
Engine harder to start (listed by OBD-Codes.com)
Decreased engine performance (listed by RepairPal)
Increased fuel consumption (listed by RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Damaged, worn or contaminated spark plug, or a faulty spark plug wire
Faulty ignition coil (coil pack)
Faulty fuel injector
Fuel supply problems: fuel pump failure, running out of fuel, or fuel that doesn't meet the manufacturer's requirements
Vacuum leak or exhaust leak (listed by RepairPal)
Engine sensor failure (listed by RepairPal)
Poor compression, a burned exhaust valve or other internal engine failure
Faulty oxygen sensor(s) or catalytic converter (listed by OBD-Codes.com only)
Defective engine computer, or PCM software that needs an update

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes and freeze frame data and write them down. If other misfire codes (P0300 to P0311) or fuel, lean or sensor codes are stored too, note them, since they change where to look.
If there are no symptoms, OBD-Codes.com says the simplest step is to clear the code and see if it comes back.
With the engine off and cool, check the wiring and connectors leading to cylinder 12's coil and spark plug, and repair any damage.
If your ignition parts are due by your maintenance schedule, OBD-Codes.com suggests replacing the spark plugs, plug wires, and distributor cap and rotor where fitted.
Inspect the cylinder 12 coil and spark plug. If they're easy to reach, swap the coil with another cylinder, clear the codes and see whether the misfire moves with it.
Make sure the tank has enough fuel of the grade your owner's manual calls for.
OBD-Codes.com notes that a rotten-egg smell from the exhaust points to a failed catalytic converter that needs replacing.

Typical fixes

Replace the spark plug, plug wire or ignition coil on cylinder 12 (RepairPal lists ignition coil replacement as a common repair)
Replace a faulty fuel injector once testing confirms it (RepairPal lists fuel injector replacement as a common repair)
Repair vacuum or exhaust leaks, or fuel pump problems
Update the PCM software if the manufacturer has released an update
Repair mechanical problems such as a burned valve or low compression found by testing
Replace a failed catalytic converter

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The check engine light is flashing
The misfire stays on cylinder 12 after replacing the plug and coil
Cylinder 12 is hard to reach, which is common on tightly packaged twelve-cylinder engines
A compression or leak-down test is needed to check valves, rings or the head gasket
Fuel injector, fuel pressure or PCM software checks that need a scan tool or dealer equipment

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0312?

RepairPal rates it 'Urgent'. A misfire can damage the catalytic converter, so limit driving, especially if the check engine light is flashing, and get it fixed soon.

Why does my car have a cylinder 12?

Only engines with twelve or more cylinders have one, so P0312 shows up far less often than codes for cylinders 1 to 6. Cylinder numbering varies by engine, so check your service information to find which cylinder is number 12.

What's the difference between P0300 and P0312?

P0312 pins the misfire to cylinder 12. P0300 means random or multiple cylinders are misfiring, which usually points to something shared by all cylinders, such as fuel pressure or a vacuum leak.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.