What causes fault code P0312?

• Most likely: Defective ignition coil (COP) or spark plug on cylinder 12 • Likely: Clogged or faulty fuel injector • Possible: Wiring harness damage or connector corrosion at cylinder 12 • Rare: Mechanical engine problem (Low compression, worn camshaft lobes, or valve issues) • Rare: Intake manifold vacuum leak specifically affecting cylinder 12

Powertrain (Engine & Gearbox)Standard EOBD

P0312 - Cylinder 12 Misfire Detected

Q: What are the symptoms of fault code P0312?

• Check Engine Light (MIL) on or flashing • Engine hesitation or jerking during acceleration • Rough idling and engine vibration • Reduced engine power and performance • Smell of raw fuel from the exhaust • Increased fuel consumption

Q: How do you fix fault code P0312?

STEP 1: Inspect spark plug and ignition coil on cylinder 12. Swap coil with a known good cylinder to see if the misfire code follows. STEP 2: Measure ignition coil primary resistance (typically 0.5-2.0 Ohms) and verify 12V supply and ground trigger. STEP 3: Perform an injector balance test. Check injector resistance (typically 12-16 Ohms) and verify pulsed signal using a Noid light. STEP 4: If ignition and fuel are OK, perform a compression test and leak-down test on cylinder 12. STEP 5: Check for intake manifold leaks or vacuum leaks specifically around the cylinder 12 intake port.

Last updated:1 February 2026

Related:Spark Plug, Ignition Coil, Fuel Injector, Crankshaft Position Sensor (CKP), Engine Control Module (ECM/PCM)

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0300

Random or Multiple Cylinder Misfire Detected

P0301

Cylinder 1 Misfire Detected

P0302

Cylinder 2 Misfire Detected

P0303

Cylinder 3 Misfire Detected

Technical Description

P0312 is a generic OBD-II diagnostic trouble code indicating that the Engine Control Module (ECM) has detected a misfire condition in cylinder number 12. The ECM monitors the crankshaft position (CKP) sensor for variations in rotational speed. If the crankshaft velocity does not increase as expected during the power stroke of cylinder 12, a misfire event is logged. A flashing Malfunction Indicator Lamp (MIL) indicates a severe misfire capable of causing catalyst damage due to unburned fuel entering the exhaust stream. This code is specific to engines with 12 or more cylinders (V12 or W12 configurations).

Possible Causes

Defective ignition coil (COP) or spark plug on cylinder 12

Clogged or faulty fuel injector

Wiring harness damage or connector corrosion at cylinder 12

Mechanical engine problem (Low compression, worn camshaft lobes, or valve issues)

Intake manifold vacuum leak specifically affecting cylinder 12

Symptoms

Check Engine Light (MIL) on or flashing

Engine hesitation or jerking during acceleration

Rough idling and engine vibration

Reduced engine power and performance

Smell of raw fuel from the exhaust

Increased fuel consumption

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P0312 - Cylinder 12 Misfire Detected

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P0312 - Cylinder 12 Misfire Detected

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