P0306 Code: Cylinder 6 Misfire Detected
Cylinder 6 is misfiring. On an inline-six it's the hot rear cylinder; on GM and Hemi V8s it can shut off.
At a glance
Severity: Moderate
- Meaning
- Cylinder 6 Misfire Detected
- System
- Ignition & Misfire · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $80–$5,000
- DIY difficulty
- Moderate
P0306 is set when the engine computer sees the crankshaft slow down each time cylinder 6 should fire, often enough to raise emissions or heat the catalytic converter. What cylinder 6 is depends on the engine. On an inline-six such as BMW's, Mercedes' or older Jeep and Toyota sixes, it is the last cylinder, tucked under the cowl where the coil bakes in heat soak and oil from a weeping valve cover gasket can collect in the plug tube. On nearly every transverse V6 it is on the front, radiator-side bank, so it is easy to reach. On GM small-block and Chrysler Hemi V8s it is the third cylinder on the passenger side, and one of the four cylinders the engine shuts off while cruising, which makes a failed deactivating lifter a real suspect.
Can I keep driving? A steady light lets you drive gently to a shop, avoiding towing and wide-open throttle. If the light flashes, pull over: unburned fuel is overheating the catalytic converter. A new tick from the passenger side of a V8 means don't wait.
How to read P0306
- P Powertrain
- 0 Generic (SAE)
- 3 Ignition / misfire
- 06 Specific fault
Symptoms
- Rough idle that smooths out somewhat above 2,500 rpm
- Misfire that is worst after a hot shutdown and restart (heat-soaked rear coil on an inline-six)
- Oil smell or smoke from the back of the valve cover on an inline-six
- Tick from the passenger-side valve cover on a GM or Hemi V8
- Check-engine light flashing when accelerating up a grade
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Heat-damaged ignition coil on cylinder 6, especially the rear coil of an inline-six under the cowl
- Oil-fouled or worn plug 6, with oil in the plug tube from a leaking valve cover or tube seal
- Failed cylinder-deactivation lifter or worn cam lobe on cylinder 6 (GM Active Fuel Management, Chrysler MDS)
- Leaking or clogged cylinder 6 injector, including leaking direct injectors on turbo sixes
- Carbon build-up on the intake valves of a direct-injection engine
- Intake gasket leak at the end runner or a cracked PCV hose near the rear of the engine
- Damaged coil or injector wiring at the rear of the harness
Diagnosis step by step
Identify which cylinder is number 6 on your engine
On an inline-six it is the one closest to the firewall. On transverse V6s from GM, Toyota, Honda and Ford it is on the front bank. On GM and Chrysler V8s it is third from the front on the passenger side, and on Ford V8s second from the front on the driver side. Getting this wrong means testing the wrong coil.
Tools: Flashlight
Pull coil 6 and look for oil
Engine off and cool, remove coil 6 and look into the plug tube. Oil means the valve cover gasket or tube seal is leaking, and the coil boot will keep failing until that seal is replaced. A brown, crusty boot or a boot that has swollen and gone soft confirms it.
Tools: Flashlight, Screwdriver
Swap coil 6 with its neighbor
On an inline-six swap it with coil 5 or 3, which sit under the same cover. On a V6 front bank use coil 2 or 4 (GM, Toyota) or 4 or 5 (Honda, Ford). Clear the code, drive until the engine is fully hot, restart after a 10-minute stop, and see whether the misfire moved. Heat-related coil failures often only show up on that hot restart.
Tools: Screwdriver, OBD-II scanner
Check the plug and plug gap
Remove plug 6 and compare its gap and color with plug 5. Wet oil on the threads or insulator matches the plug-tube leak. On turbocharged direct-injection sixes, a gap that has opened only a few thousandths of an inch beyond spec is enough to cause a misfire under boost.
Tools: Spark plug socket, Torque wrench
On a GM or Hemi V8, watch the cylinder 6 rockers
Remove the passenger-side valve cover and have a helper bump the starter while you watch cylinder 6's intake and exhaust rocker arms. Both should move as far as those on cylinders 2 and 4. A rocker that barely moves or has play at rest points to a collapsed lifter or a flattened cam lobe.
Tools: Screwdriver, Flashlight
Run an injector balance or cut-out test
If ignition checks out, use a bidirectional scan tool to cut each injector in turn and compare the rpm drop. On a turbo direct-injection six, also watch whether cylinder 6's fuel trim or misfire count gets worse after a cold start, which points to an injector that drips while the engine sits.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace cylinder 6 coil and boot | Yes | $80–$280 |
| Replace valve cover gasket and plug tube seals (inline-six) | No | $250–$750 |
| Replace spark plugs, full set of six | Yes | $150–$450 |
| Replace cylinder 6 direct injector | No | $350–$900 |
| Replace lifters and camshaft (GM AFM / Hemi MDS V8) | No | $2,200–$5,000 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
BMW
On BMW N52, N54 and N55 inline-sixes, an aging valve cover gasket lets oil into the plug tubes and onto the exhaust side. Cylinder 6 sits at the hot rear end, and oil-soaked coil boots there are a common cause of P0306. Replacing only the coil without the gasket usually buys a few months at most.
Chevrolet
On GM 5.3L and 6.2L V8s with Active Fuel Management, cylinder 6 is one of the four deactivated cylinders. A P0306 with a tick, a coil and plug that check out, and higher mileage is a textbook case for a failed AFM lifter. Inspect the rockers before buying ignition parts.
Ram
The 5.7L Hemi shuts off cylinders 1, 4, 6 and 7 with its Multi-Displacement System. Lifter roller and cam lobe wear, heard as the familiar Hemi tick, can cause a persistent P0306. Remember each Hemi cylinder has two spark plugs, so replace both.
Field data
| Honda | 12 | Pilot, Odyssey, Ridgeline | |
|---|---|---|---|
| Ford | 10 | F-150 SUPERCAB, F-150 SUPER CREW, Escape | |
| Jeep | 9 | Wrangler Unlimited, Wrangler, Grand Cherokee | |
| Kia | 7 | Sedona, Sorento | |
| Chrysler | 6 | Pacifica, 200 | |
| Dodge | 5 | Grand Caravan, Avenger, Durango | |
| GMC | 5 | Acadia, Sierra 1500, Sierra 1500 Hybrid | |
| Toyota | 3 | Avalon, Highlander Hybrid, RAV4 |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
An active P0306 with the check-engine light on fails OBD emissions testing. If the repair was a lifter or cam job, drive several days of mixed city and highway miles so the misfire and catalyst monitors show ready before you retest.
Frequently asked questions
Why is cylinder 6 on my BMW so often the one that misfires?
It sits at the back of the engine, right under the cowl, where heat builds up after shutdown and where oil from a leaking valve cover gasket tends to pool. Both shorten the life of the coil boot. Fix the oil leak and the rear coil lasts much longer.
Could P0306 on my Silverado be a lifter even though the engine runs okay most of the time?
Yes. On AFM engines a lifter can start by sticking only occasionally, often when the engine switches in or out of V4 mode. Early on the misfire comes and goes; later the lifter collapses fully and the tick becomes constant.
Is cylinder 6 hard to reach on a V6?
On most transverse V6s it's on the front bank and takes minutes to reach. On rear-wheel-drive trucks with a V6, it is often at the rear of one bank near the firewall, where you may need a long extension and a swivel socket.
The misfire only happens on a hot restart. What does that mean?
That pattern points strongly to a coil whose windings crack or short when heat-soaked. Swap it with another cylinder and test again on a hot restart. If the misfire follows it, replace the coil.