P0307
Cylinder 7 Misfire Detected
When a vehicle powertrain module registers the fault code P0307, it points directly to an internal system malfunction identified as "Cylinder 7 Misfire Detected". Operating your engine under this condition may degrade long-term fuel maps.
Driver's Summary
Your vehicle's computer logged P0307 after detecting a malfunction in the cylinder 7 misfire detected system. Drivers typically experience flashing mil, hesitation under load, poor gas mileage when this code is active. Stop driving as soon as it is safe to do so. This fault can lead to expensive secondary damage if left unaddressed.
Symptoms
Flashing MIL, hesitation under load, poor gas mileage
Common Causes
- Worn spark plug
- Ignition coil failure
- Vacuum leak near cylinder 7
- Internal engine damage
How to Fix
- 1 Change spark plug
- 2 Replace ignition coil
- 3 Inspect vacuum hoses
- 4 Perform leak down test
Technical Explanation
Detection of P0307 occurs when the ECM cross-references multiple sensor inputs and determines that the reported values are physically inconsistent or out-of-range. Misfire rate is counted per cylinder over rolling windows and compared against two thresholds: a catalyst-damaging rate (triggers flashing MIL) and an emissions-exceeding rate (triggers solid MIL). The PCM logs which cylinder is misfiring based on crankshaft position at the time of each detected event. The fault remains stored in memory even after the MIL is cleared; it becomes a confirmed DTC after failing two consecutive drive cycles, and the PCM logs a freeze frame record of the engine's exact operating state at the moment of detection.
Is It Safe to Drive?
Driving with an active P0307 fault risks accelerating damage to worn spark plug and related components. The longer the fault persists, the more expensive the eventual repair becomes — what starts as a sensor or solenoid issue can escalate to major mechanical failure.
Mechanic's Pro Tip
For P0307, always perform a smoke test before replacing any parts — unmetered air from a cracked intake boot, split hose, or failed gasket is the root cause in the majority of lean fault cases and costs almost nothing to fix. After any repair, clear the code and watch short-term fuel trim (STFT) live on a scan tool; it should recover to within ±5% at idle within 2–3 minutes if the vacuum leak is truly resolved.
Plug/Coil: $100 - $300; Internal repair: $1,000 - $1,500+