What it means
Misfires concentrated on cylinder 11. A cylinder-specific code points away from shared causes (fuel pressure, MAF) toward components dedicated to that cylinder — coil, spark plug, injector, compression.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine controller estimates misfires by tracking crankshaft speed changes as each cylinder fires. P0311 is set when that monitoring identifies repeated combustion misses at cylinder 11, directing attention to that cylinder’s ignition, fuel delivery, and compression.
Common causes
Most likely first.
- Faulty spark plug or ignition coil for cylinder 11
- Clogged or faulty cylinder 11 fuel injector
- Damaged wiring or connector at the cylinder 11 ignition or injector
- Low compression in cylinder 11
Symptoms
- Check engine light on or flashing
- Rough idle and uneven running
- Power loss, hesitation under acceleration
- Increased fuel consumption
- Possible smell of unburned fuel from exhaust
How to diagnose it
- Read freeze-frame data and misfire counts to confirm the fault occurred at cylinder 11 and note the engine temperature and load.
- Inspect cylinder 11’s spark plug, ignition coil, injector connector, and nearby wiring for damage, looseness, or contamination.
- If the engine uses interchangeable coils, swap cylinder 11’s coil with another cylinder and see whether the misfire follows the coil.
- Check the cylinder 11 spark plug and injector operation using the vehicle’s service information and compare results with other cylinders.
- If the misfire stays at cylinder 11, perform a compression or leak-down test and compare the result with the manufacturer’s specification.
Common fixes
- Repair a loose or damaged cylinder 11 connector or wire.
- Replace a worn or fouled cylinder 11 spark plug.
- Replace a faulty cylinder 11 ignition coil if the misfire follows it during a swap test.
- Clean or replace a cylinder 11 injector if testing confirms poor delivery.
- Repair the cause of low cylinder 11 compression.
Can I keep driving?
If the check engine light is flashing, stop driving as soon as it is safe; continued misfiring can overheat and damage the catalytic converter. With a steady light and mild symptoms, drive only gently to a repair location, since power loss and fuel use may increase.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.