Why is cylinder 6 more expensive to fix than cylinder 1?

Access. On many transverse V6 engines, cylinder 6 is behind the engine near the firewall. Reaching the spark plug or coil requires significant disassembly.

Can P0306 on a V6 be a valve cover gasket leak?

Yes. Oil leaking from the valve cover gasket into the spark plug well can short out the coil and foul the plug, both causing a misfire on that cylinder.

Should I replace all six plugs or just the one on cylinder 6?

If mileage is high and plugs have not been done, replace all of them while you have access. One failed plug often means the others are not far behind.

Codes › P0306

P0306: Cylinder 6 is misfiring

Cylinder 6 Misfire Detected

High severityCan you keep driving?

If the light is flashing, stop now. Do not drive on a misfiring cylinder. If the light is steady and the car is shaking, go straight to a shop. Driving with this code risks destroying the catalytic converter.

What it means

P0306 means cylinder 6 is not completing combustion reliably. Cylinder 6 exists on V6, V8, and larger engines. On a V6, cylinder 6 is at the rear of Bank 2, which is often near the firewall on front-wheel-drive vehicles. Accessing cylinder 6 on a transversely mounted V6 can be genuinely difficult and is where labor costs climb for what would otherwise be an inexpensive ignition repair. On V8 engines, cylinder 6 is typically the second from the rear on one bank and is somewhat more accessible than cylinder 8.

Common causes

Failed ignition coil on cylinder 6Coil failure is the leading cause. Swap and road test to confirm before buying a part.
Worn spark plug on cylinder 6On transverse V6 engines, rear-bank plugs are often skipped at service intervals due to access difficulty.
Failed or clogged fuel injector on cylinder 6Check for P0206 in the stored codes.
Low compression on cylinder 6More common at high mileage. Compression test required.
Water or carbon in the intake on cylinder 6Direct-injection engines accumulate carbon on intake valves, causing intermittent lean misfires.

What it costs

Spark plug set$100 to $400 (higher on difficult-access V6)
Ignition coil (one)$150 to $500 installed (access labor varies widely)
Fuel injector (one)$150 to $450 installed
Compression repair$900 to $3,500

Symptoms

Check engine light flashing or steady
Engine vibration at idle and low speed
Hesitation or stumble on acceleration
Power loss
Possible fuel smell from exhaust

What to do next

Get a labor estimate before you start if your V6 has rear-bank access issues. On some vehicles (Chrysler 3.5L, GM 3.6L), replacing rear-bank spark plugs requires removing the intake manifold and can cost $500 or more in labor alone. Confirm the diagnosis with a coil swap before committing to full spark plug replacement if the car is a known difficult-access engine.

Lewis shows cylinder 6 misfire counts per 1,000 revolutions so you can see if it is a constant failure or an intermittent one linked to temperature or load. Download Lewis.

Related codes

FAQ

Why is cylinder 6 more expensive to fix than cylinder 1?: Access. On many transverse V6 engines, cylinder 6 is behind the engine near the firewall. Reaching the spark plug or coil requires significant disassembly.
Can P0306 on a V6 be a valve cover gasket leak?: Yes. Oil leaking from the valve cover gasket into the spark plug well can short out the coil and foul the plug, both causing a misfire on that cylinder.
Should I replace all six plugs or just the one on cylinder 6?: If mileage is high and plugs have not been done, replace all of them while you have access. One failed plug often means the others are not far behind.