P0304
Cylinder 3 Misfire Detected
Powertrain Ignition System Cylinder Misfire 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Cylinder 3 is misfiring, meaning its spark plug isn't igniting the fuel-air mixture reliably. It's like one piston in a 4-cylinder engine occasionally refusing to fire, causing rough running and lost power.

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Symptoms You May Notice
3 known symptoms for this code
Rough idle or engine vibration
Check Engine Light illuminated
Loss of power and fuel economy
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors crankshaft speed variation using the crank sensor to detect when a cylinder fails to combust. When cylinder 3 misfires, it creates a detectable dip in engine speed. The threshold is typically exceeded after a certain number of misfire events within a driving cycle.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Crankshaft RPM Variation Smooth acceleration without drops Intermittent speed loss on cylinder 3 firing stroke
Misfire Count 0-2 misfires per 1000 revolutions 3+ 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 3 spark plug for wear or fouling; replace if gap is incorrect or electrode is damaged.
2
Ignition Coil Pack
Test or replace the ignition coil assigned to cylinder 3 if spark plug is good.
3
Fuel Injector
Clean or replace cylinder 3 fuel injector if fuel delivery is weak or clogged.