P0306
Cylinder 6 Misfire Detected
If your vehicle's onboard computer has flagged the diagnostic trouble code P0306, it refers to a detected anomaly regarding "Cylinder 6 Misfire Detected". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
P0306 is triggered when the PCM detects an abnormal condition associated with cylinder 6 misfire detected. On the road, this usually shows up as rough idle, poor acceleration, noticeable vibration. Given the high severity of this code, continuing to drive risks significant mechanical damage. Have it diagnosed immediately.
Symptoms
Rough idle, poor acceleration, noticeable vibration
Common Causes
- Defective spark plug or wire
- Faulty coil on plug
- Intake manifold gasket leak
- Bad fuel injector
How to Fix
- 1 Replace cylinder 6 spark plug and boot
- 2 Test and replace ignition coil
- 3 Spray carburetor cleaner to check for intake leaks
- 4 Test injector resistance
Technical Explanation
The PCM triggers P0306 after its internal monitoring routine detects that a specific circuit or sensor has exceeded its acceptable operating range. The PCM monitors crankshaft rotational velocity via the CKP sensor at a resolution of individual tooth gaps on the reluctor ring. A combustion event in each cylinder produces a measurable acceleration spike; its absence or weakness is flagged as a misfire event within a 200-revolution or 1000-revolution test window. Once confirmed, the code is stored as a permanent DTC and the MIL is activated. The freeze frame snapshot — recording RPM, load, coolant temperature, and fuel trim at fault detection — is also saved and is critical for accurate diagnosis.
Is It Safe to Drive?
With P0306 active, your engine or transmission is not operating within design parameters. Short-term driving may seem fine, but internal damage is accumulating — particularly to defective spark plug or wire.
Mechanic's Pro Tip
For P0306, 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.
Coil replacement: $150 - $300; Intake gasket: $300 - $700