P0312 high Severity

P0312: Cylinder 12 Misfire Detected

Rough idle, loss of power, possible stalling, increased emissions and potential catalytic converter damage

Overview

P0312 indicates that the powertrain control module (PCM/ECM) has detected a misfire in cylinder 12 of the engine, which can stem from ignition, fuel delivery, compression, or sensor/electrical issues.

Common Symptoms

  • Check engine light illuminated
  • Rough engine idle
  • Engine vibration or hesitation
  • Loss of power or poor acceleration
  • Decreased fuel efficiency

Most Common Causes

Faulty spark plug in cylinder 12 high

Spark plug wear or fouling often leads to misfires in the affected cylinder.

Defective ignition coil for cylinder 12 high

Ignition coil failure prevents proper spark, leading to misfire.

Fuel injector malfunction (clogged or failed) medium

Fuel delivery issues can cause a lean condition, leading to misfire.

Low compression in cylinder 12 medium

Internal engine issues (valve, piston rings) reducing cylinder pressure.

Wiring or connector issues at cylinder 12 components medium

Poor electrical connection can disrupt ignition or fuel injector control.

Vacuum leak near cylinder 12 low

Vacuum leaks can alter air/fuel mixture and induce misfire conditions.

ECM/PCM software or module error low

Rarely, module misinterpretation or internal fault can log the code incorrectly.

Diagnostic Steps

  1. Use a professional OBD‑II scan tool to confirm the presence of P0312 and check for any related codes.
    Expected: Confirmed P0312 with misfire counts for cylinder 12; possible additional codes.
    Interpretation: Establish that the misfire is isolated to cylinder 12.
  2. Inspect spark plug and ignition coil for cylinder 12.
    Expected: Visual wear, fouling, or damage; poor spark.
    Interpretation: Faulty ignition components support misfire cause.
  3. Perform swap test of ignition coil and spark plug with another cylinder.
    Expected: Misfire follows part if part is faulty.
    Interpretation: Isolates defective ignition component.
  4. Check fuel injector operation on cylinder 12 (listening for click, resistance test).
    Expected: No injector activation or abnormal resistance indicates injector fault.
    Interpretation: Fuel delivery issue contributing to misfire.
  5. Perform compression test on cylinder 12 and compare to other cylinders.
    Expected: Significantly lower compression in cylinder 12.
    Interpretation: Mechanical issue such as worn rings or valve problem.
  6. Inspect wiring/connectors and check for vacuum leaks near cylinder 12.
    Expected: Loose connectors, corrosion or visible leaks.
    Interpretation: Electrical or vacuum issues affecting combustion.

Repair Solutions

Replace spark plug for cylinder 12 easy
Estimated Cost: $10 - $50

Standard maintenance item; often resolves simple misfires.

Replace ignition coil for cylinder 12 medium
Estimated Cost: $50 - $200

Ignition coil replacement can require minor labor.

Clean or replace fuel injector for cylinder 12 medium
Estimated Cost: $100 - $600

Injector issues may require professional tools.

Repair vacuum leaks near intake manifold medium
Estimated Cost: $50 - $300

Depends on extent and location of leak.

Engine mechanical repair (e.g., valve or piston work) hard
Estimated Cost: $500 - $5000

Internal engine issues require advanced diagnostics and labor.

ECM/PCM reflash or replacement hard
Estimated Cost: $200 - $1000

Rare; only after verifying module fault.

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Interpreting a random misfire code (P0300) as P0312 without specific cylinder analysis
  • Replacing oxygen sensors instead of addressing cylinder‑specific ignition/fuel issues
  • Assuming ECM failure without verifying ignition and fuel components first

Frequently Asked Questions

What is the definition of the P0312 engine code?

When your OBD-II scanner reads P0312, it means: Cylinder 12 Misfire Detected. This code is related to the vehicle's Ignition.

How serious is the P0312 code?

This is a high priority issue. Rough idle, loss of power, possible stalling, increased emissions and potential catalytic converter damage

What are the symptoms of P0312?

Common symptoms include: Check engine light illuminated, Rough engine idle, Engine vibration or hesitation. You might also notice the Check Engine Light is on.

Common triggers for the P0312 error

This code is frequently triggered by: Faulty spark plug in cylinder 12, Defective ignition coil for cylinder 12, Fuel injector malfunction (clogged or failed).

Estimated repair costs for different causes of P0312

It depends on what needs to be fixed. Replace spark plug for cylinder 12 repairs are cheaper (~$50), while Engine mechanical repair (e.g., valve or piston work) repairs are on the higher end (~$5000).

Is the P0312 code specific to Dodge?

Yes, P0312 is a generic code that applies to all OBD-II compliant vehicles, including Ford, Toyota, Honda, Chevrolet, Nissan, Dodge, BMW, and more.

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