Faulty or fouled spark plug on cylinder 1, especially from oil or carbon deposits; Weak or failing ignition coil on cylinder 1 that breaks down under cold, damp startup conditions; Leaking or clogged fuel injector on cylinder 1 causing an incorrect air-fuel mixture during cold start; Intake manifold gasket leak or vacuum leak near cylinder 1 that leans out the mixture only when cold; Low compression on cylinder 1 from worn rings, valve seats, or a sticking valve; Carbon buildup on intake valves, a common BMW issue that disrupts cold-start mixture on direct-injection engines; Faulty engine coolant temperature sensor sending an incorrect cold-start signal to the engine control module

DTC codes / BMW codes / P1342

P1342 · BMWMisfire During Start Cylinder 1

Q: What does code P1342 mean?

Misfire During Start Cylinder 1. P1342 on BMW vehicles means the engine control module detected a misfire specifically during the startup phase on cylinder 1, typically within the first few hundred revolutions after cranking. The computer monitors crankshaft speed fluctuations and flags this code when cylinder 1 fails to contribute its expected power during that initial firing window, even if the engine runs smoothly once warmed up.

P1342 on BMW vehicles means the engine control module detected a misfire specifically during the startup phase on cylinder 1, typically within the first few hundred revolutions after cranking. The computer monitors crankshaft speed fluctuations and flags this code when cylinder 1 fails to contribute its expected power during that initial firing window, even if the engine runs smoothly once warmed up.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Rough idle or shaking immediately after a cold start that often clears within seconds
A flashing or steady check engine light, sometimes accompanied by reduced engine power
Noticeable hesitation or stumble when cranking, especially in cold weather
Occasional hard starting or extended crank time before the engine catches
Often no symptoms besides the warning light once the engine is running normally

Common causes, most likely first

Faulty or fouled spark plug on cylinder 1, especially from oil or carbon deposits
Weak or failing ignition coil on cylinder 1 that breaks down under cold, damp startup conditions
Leaking or clogged fuel injector on cylinder 1 causing an incorrect air-fuel mixture during cold start
Intake manifold gasket leak or vacuum leak near cylinder 1 that leans out the mixture only when cold
Low compression on cylinder 1 from worn rings, valve seats, or a sticking valve
Carbon buildup on intake valves, a common BMW issue that disrupts cold-start mixture on direct-injection engines
Faulty engine coolant temperature sensor sending an incorrect cold-start signal to the engine control module

How to diagnose and fix it

Scan all modules for stored and pending fault codes, then record freeze-frame data to confirm the misfire occurs only during startup
Inspect the cylinder 1 spark plug for fouling, wear, or incorrect gap and replace it if worn or contaminated
Swap the cylinder 1 ignition coil with a known-good coil from another cylinder and recheck for a code change to isolate a weak coil
Perform a cold-start fuel trim and injector balance test to check for a leaking or clogged injector on cylinder 1
Run a compression test and, if low, a cylinder leak-down test on cylinder 1 to rule out mechanical faults
Smoke-test the intake system for vacuum leaks near cylinder 1 and inspect the intake manifold gasket
Check the engine coolant temperature sensor reading against actual ambient temperature when cold and replace if skewed

Cold-start misfires that hide when warm

A P1342 that only appears on the first start of the day often points to a coil or plug that breaks down under cold, damp conditions rather than a failed component that would misfire constantly.
BMW direct-injection engines commonly develop carbon buildup on intake valves, which can cause a startup misfire on one cylinder even when the plug and coil test good.
Technicians sometimes replace all coils and plugs only to find the real cause is a slightly leaking injector that drips fuel into cylinder 1 overnight and fouls the plug on the first start.
A weak battery or slow cranking can trigger a startup misfire code because the engine control module sees inconsistent crankshaft speed during the first few revolutions, so always check battery health and cranking voltage.
This code does not always mean the misfire continues once the engine is running; if the misfire counter stops after startup, focus diagnosis on cold-start enrichment and ignition components rather than a constant mechanical fault.

Can I keep driving with P1342?

You can usually drive the car if the misfire clears once the engine is warm and the check engine light is steady, but avoid hard acceleration and long trips until it is diagnosed. If the light flashes or the engine runs rough continuously, stop driving to prevent unburned fuel from damaging the catalytic converter.

Tools that help

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Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.