P1343
Misfire Cylinder 1 With Fuel Cut-off.
- BMW
- Powertrain
- Manufacturer code
- High severity
How this code is built
- P
- SystemPowertrain
- 1
- Defined byThe manufacturer
- 3
- AreaIgnition system or misfire
- 43
- FaultThe specific fault in that area
What it means
On BMW, P1343 means the engine control unit detected misfires on cylinder 1 severe enough that it has cut the fuel to that cylinder to protect the catalytic converter. The control unit saw crankshaft speed irregularities attributed to cylinder 1 above its damage threshold. The exact trigger and strategy can vary by engine family, so confirm against model-specific information.
Symptoms
- Engine running rough, shaking or hesitating, especially at idle
- Flashing or steady engine warning light
- Loss of power and poor acceleration
- Smell of unburnt fuel from the exhaust
- Engine running on fewer cylinders with a noticeably uneven note
- Reduced engine performance or limp-style response
Possible causes
- Worn or faulty spark plug on cylinder 1likely
- Failed or weak ignition coil on cylinder 1likely
- Faulty or leaking fuel injector on cylinder 1, or its wiring or connectorpossible
- Vacuum or intake air leak affecting cylinder 1, such as a split intake boot or leaking gasketpossible
- Low compression on cylinder 1 from a valve, piston ring or head gasket problemrare
- Wiring or connector fault in the cylinder 1 ignition or injector circuitpossible
How to diagnose
- Read all stored codes and freeze frame data, noting engine load, speed and temperature when the fault set, and check for other misfire or fuel trim codes
- Inspect the cylinder 1 coil connector, wiring and injector connector for damage, corrosion or oil contamination
- Remove the cylinder 1 spark plug and inspect its condition and gap against the others
- Swap the cylinder 1 coil with another cylinder, clear the codes, and see whether the misfire follows the coil
- If the misfire stays on cylinder 1, check the injector with a resistance test and listen for operation, following model-specific procedures
- Inspect the intake system for leaks and check fuel trims for signs of a lean condition
- Carry out a compression or leak-down test on cylinder 1 if ignition and fuel causes are ruled out
- Check live misfire counters to confirm the repair holds after a road test
How to fix
- Replace the spark plugs as a set, using the correct specification for the engine
- Replace the faulty ignition coil on cylinder 1
- Replace or professionally clean the faulty fuel injector, as the manufacturer advises
- Repair damaged wiring or connectors in the cylinder 1 circuits
- Repair intake leaks by replacing split hoses or faulty seals
- Carry out the necessary mechanical engine repair if compression is low
Can I keep driving?
High severity
Avoid driving it, or keep it to a minimum at low load, because continued misfiring can overheat and damage the catalytic converter. Get it diagnosed promptly, and stop driving if the warning light is flashing.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.