OBD Code P0320: Cylinder 12 Misfire Detected

Q: What does OBD code P0320 mean?

Cylinder 12 Misfire Detected. The engine's computer detected that cylinder 12 isn't firing properly, like a car with a dead spark plug that causes a stumble. This misfiring reduces power and increases emissions.

Q: What are the symptoms of fault code P0320?

Rough idle or engine stumbling, Reduced fuel economy and power loss, Check Engine Light illuminated

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What This Actually Means

In plain language — no jargon

The engine's computer detected that cylinder 12 isn't firing properly, like a car with a dead spark plug that causes a stumble. This misfiring reduces power and increases emissions.

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Symptoms You May Notice

3 known symptoms for this code

Rough idle or engine stumbling

Reduced fuel economy and power loss

Check Engine Light illuminated

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Embedded Systems Insight

What the ECU/ECM is actually computing

The ECM monitors crankshaft speed variations using the crank sensor to detect misfires. When a cylinder fails to fire, it creates a distinct dip in RPM that the ECU recognizes as a misfire event. If misfire counts exceed the threshold, the fault code sets.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
Crankshaft acceleration variance	Consistent RPM without dropouts	>2-4% RPM deviation per cylinder event
Cumulative misfire count	<2 misfires per 1000 revolutions	>4 misfires per 1000 revolutions

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Spark plug

Remove and inspect cylinder 12 spark plug for wear or fouling; replace if gap is incorrect or electrode is damaged.

2

Ignition coil

Test or swap the ignition coil for cylinder 12 to rule out coil failure causing weak spark.

3

Fuel injector

Clean or replace the fuel injector for cylinder 12 if fuel delivery is restricted or spray pattern is poor.