P1342
Misfire During Start Cylinder 1.
- BMW
- Powertrain
- Manufacturer code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 1
- Defined byThe manufacturer
- 3
- AreaIgnition system or misfire
- 42
- FaultThe specific fault in that area
What it means
On BMW, P1342 means the engine control unit detected misfiring on cylinder 1 during engine start. It sets when crankshaft speed signals show a drop in acceleration contribution from that cylinder in the starting phase, which points to poor combustion there. This is the BMW definition only and differs from the Volkswagen meaning of the same number.
Symptoms
- Rough or shaky running straight after a cold or warm start
- Engine cranks longer than normal or starts reluctantly
- Engine management warning light on, possibly flashing under load
- Noticeable hesitation or loss of power just after starting
- Raw fuel smell from the exhaust at start-up
Possible causes
- Worn or faulty spark plug on cylinder 1likely
- Failing ignition coil on cylinder 1 (internal fault or cracked boot)likely
- Faulty or leaking fuel injector on cylinder 1, or injector wiring or connector faultpossible
- Low compression on cylinder 1 (valve, piston ring or head gasket issue)possible
- Air leak or vacuum leak affecting the mixture, or fuel pressure problem; details depend on engine variantpossible
- Faulty crankshaft position sensor or damaged reluctor signal causing false misfire detectionrare
How to diagnose
- Read all stored codes and freeze frame data, noting engine temperature, load and whether other cylinders also show misfires
- Check misfire counters or live data for cylinder 1 if the diagnostic equipment supports it
- Inspect the coil, connector and wiring on cylinder 1 for damage, moisture, oil contamination or corrosion
- Remove and inspect the cylinder 1 spark plug for wear, fouling, damage or the wrong gap, and compare with the others
- Swap the cylinder 1 coil with another cylinder, clear the codes and see whether the misfire follows the coil
- Check the injector connector and wiring, and test injector operation and fuel pressure as the engine type requires
- Inspect for intake air leaks and check for split hoses or loose fittings
- Carry out a compression or leak-down test on cylinder 1 if the ignition and fuel side checks out
How to fix
- Replace the spark plugs as a set with the correct type for the engine
- Replace the faulty ignition coil on cylinder 1
- Repair damaged wiring or connectors to the coil or injector
- Replace the faulty fuel injector on cylinder 1 after confirming the fault
- Repair or replace the leaking intake component, hose or seal found during testing
- Carry out the necessary mechanical engine repair if compression is low
Can I keep driving?
Medium severity
The car can be driven gently for a short time to get it repaired, but avoid heavy loads. If the warning light flashes, reduce power and stop driving as soon as it is safe, because raw fuel can damage the catalytic converter.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.