P0314

What it means

P0314 is the generic code for a misfire that the engine control unit has traced to a single cylinder, with the specific cylinder not stored by this code. It is set when crankshaft speed monitoring shows repeated, abnormal speed fluctuations from one cylinder's firing events, and it is normally stored together with a cylinder-specific misfire code such as P0301 to P0308, or after the cylinder has been identified. It is an additional code that points to an ignition, fuel, air or mechanical fault affecting just one cylinder.

Symptoms

• Rough or uneven idle, often with a noticeable shake
• Hesitation, juddering or loss of power under load
• Flashing or constant engine warning light
• Smell of unburnt fuel from the exhaust
• Poor fuel economy
• Difficult starting or occasional stalling

Possible causes

• Worn, fouled or incorrectly gapped spark plug on one cylinderlikely
• Faulty ignition coil or coil connector on one cylinderlikely
• Faulty, blocked or leaking fuel injector on one cylinderlikely
• Vacuum or intake leak affecting one cylinder, such as a split intake manifold seal or runner gasketpossible
• Low compression in one cylinder from a burnt valve, worn piston rings or a damaged head gasketpossible
• Damaged wiring or poor connection to the injector or coil of one cylinderpossible
• Valvetrain fault on one cylinder, such as a worn cam lobe, collapsed lifter or sticking valve (depends on engine)rare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting engine load, speed and temperature when the misfire occurred, and check for a cylinder-specific misfire code.
2. Check live misfire counters per cylinder if the scan equipment supports them, to identify which cylinder is affected.
3. Inspect the coil, injector connectors and wiring for the affected cylinder for damage, corrosion, oil contamination or looseness.
4. Remove and inspect the spark plug of the affected cylinder, checking condition, gap and signs of oil, fuel or overheating.
5. Swap the coil (and plug if appropriate) with a neighbouring cylinder, clear the codes and see whether the misfire follows the part.
6. Test the injector's electrical resistance and operation, and listen for a firing click or check the drive signal as the manufacturer specifies.
7. Check for intake leaks around the manifold and runner seals, for example with a smoke test.
8. Carry out a compression test or cylinder leak-down test on the affected cylinder if ignition and fuel causes are ruled out.

How to fix

• Replace the faulty spark plug, using the correct specification for the engine, and consider replacing the set if they are due.
• Replace the faulty ignition coil or repair its connector.
• Replace or professionally clean and test the faulty fuel injector, as the manufacturer recommends.
• Repair damaged wiring or connectors, or replace perished intake seals and gaskets that are letting in unmetered air.
• Carry out the necessary mechanical engine repair, such as valve, piston ring or head gasket work, if compression is low.

Can I keep driving?

Nearby codes

• P0313GenericMisfire Detected With Low Fuel
• P0315GenericCrankshaft Position System Variation Not Learned