P0308
Cylinder 7 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 7 isn't firing properly, like one spark plug in an 8-cylinder engine misfiring intermittently. The engine computer detected the cylinder isn't contributing power strokes consistently.

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

The ECU monitors crankshaft acceleration using the crankshaft position sensor to detect when a cylinder fires. If cylinder 7 shows abnormally low acceleration during its power stroke compared to baseline, it registers a misfire. The ECM counts misfire events and sets a fault when threshold is exceeded.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Crankshaft acceleration variance Consistent 3-5% variation between cylinders >10% deviation on cylinder 7 over 200 revolution window
Misfire event count 0-2 misfires per 1000 revolutions >8 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 7 spark plug for wear or fouling; replace if gap is >0.040 inches or electrode is eroded.
2
Ignition coil pack
Swap the ignition coil from cylinder 7 with another cylinder coil and retest; if code moves, coil is faulty.
3
Fuel injector
Listen for injector clicking at cylinder 7; if silent, test injector resistance with multimeter (10-16 ohms typical) or replace if open.