P0305
Cylinder 4 Misfire Detected
Powertrain Ignition System Cylinder misfire detection 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Cylinder 4 isn't firing properly—think of it like one cylinder in a 4-cylinder engine refusing to do its job. The engine detects inconsistent combustion in that specific cylinder, causing rough running and power loss.

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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 between cylinder firings using the crankshaft position sensor. When cylinder 4 misfires, it causes irregular acceleration and deceleration of the crankshaft. The ECM detects this deviation from expected combustion patterns and triggers the fault.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Crankshaft acceleration variance Consistent 1-2% variance between cylinders Exceeds 5-10% variance on cylinder 4
Ignition timing/combustion stability Stable fuel burn within ±5° crank angle Unstable or missing combustion events
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Spark plug for cylinder 4
Remove and inspect for wear, gap, or fouling; replace if worn or damaged.
2
Ignition coil for cylinder 4
Swap with another cylinder's coil to isolate; replace if fault moves or persists.
3
Fuel injector for cylinder 4
Test resistance and spray pattern; clean or replace if clogged or electrically faulty.