P0312

Universal

Cylinder 12 Misfire Detected

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
High Severity

The engine computer detected that cylinder 12 is not contributing power consistently. It typically identifies a misfire by monitoring small changes in crankshaft speed; those changes indicate uneven combustion, but do not prove that any particular part has failed. Depending on severity, the engine may run roughly, lose power, use more fuel, or produce higher emissions. Exact applicability depends on the vehicle's model, year, and engine.

Report an error with this code

⚠️ Before You Begin (Safety First)

A severe misfire can overheat and damage the catalytic converter. If the check-engine light is flashing, the engine is shaking badly, power drops substantially, or you notice fuel smell, stop driving when it is safe and arrange professional help. Avoid touching hot or moving engine parts during checks.

Common Symptoms

  • The engine may idle or run roughly if cylinder 12 is contributing unevenly.
  • Hesitation, reduced power, or poor acceleration may occur because the affected cylinder produces less power.
  • Fuel economy may worsen when combustion is incomplete.
  • The check-engine light may come on or flash; flashing can indicate a misfire severe enough to risk catalytic-converter damage.
  • Some vehicles may show no noticeable symptoms, particularly if the misfire is intermittent or mild.

Common Causes

  • A problem with the cylinder's ignition components or their electrical connections may prevent a reliable spark.
  • An injector, fuel supply, or injector circuit problem may prevent the cylinder from receiving the correct fuel delivery.
  • Low compression or another mechanical condition may prevent the cylinder from combusting normally.
  • A wiring, connector, or control problem may interrupt signals or operation in an ignition or fuel system.
  • An air leak or another condition affecting the cylinder's air-fuel mixture may contribute to uneven combustion.

Diagnostic Steps

  1. Check the owner's manual for the check-engine light guidance. If the light is flashing or the engine is running very roughly, stop driving when safe and arrange diagnosis.
  2. With the engine off and cool, look for loose or visibly damaged connectors and wiring around accessible engine components. Do not pull on wiring or touch hot or moving parts.
  3. If you have a scan tool, record all stored codes and available freeze-frame information before clearing anything; other codes may help explain when or why the misfire occurs.
  4. Use vehicle-specific service information to confirm whether the engine has a cylinder 12 and locate it. Do not assume cylinder numbering from a generic diagram.
  5. If the code returns or symptoms persist, have a technician test the relevant ignition, fuel, wiring, and mechanical systems before replacing parts.

When to Call a Professional

Confirm that the engine has a cylinder 12 and identify it using vehicle-specific service information. A technician can review stored codes and freeze-frame data, check misfire counters and relevant scan data, and test ignition, fuel delivery, wiring, and cylinder condition as indicated. The results should guide repairs rather than replacing parts based on the code alone.

Compare component listings

Confirm diagnosis and vehicle fitment before buying. A listing does not prove that a part needs replacement. We may earn a commission from qualifying purchases.

Search Amazon Search eBay

Commonly Asked Questions

Does P0312 prove that an ignition part has failed?

No. It reports a detected misfire in cylinder 12, not the failed part. Ignition, fuel delivery, wiring, air-fuel mixture, or mechanical problems can all contribute.

How does the vehicle detect a cylinder misfire?

The engine computer monitors crankshaft speed changes. Uneven changes can indicate that a cylinder is not producing its expected share of power, but further tests are needed to identify the cause.

Can I keep driving with P0312?

A mild or intermittent misfire may have few obvious effects, but continued misfiring can damage the catalytic converter. Stop when safe and seek help if the check-engine light flashes, the engine shakes severely, power drops, or fuel smell is present.

What if my engine does not have a cylinder 12?

Applicability depends on the engine and vehicle. Confirm the cylinder layout and code interpretation using service information for the exact model, year, and engine before attempting a repair.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.