Worn or fouled spark plug on cylinder 4, especially common on turbocharged BMW engines with direct injection; Faulty ignition coil on cylinder 4, which often fails intermittently when cold; Leaking or clogged fuel injector on cylinder 4, causing an incorrect air-fuel mixture during start; Carbon buildup on intake valves, a known issue on BMW direct-injection engines that affects cold-start mixture quality; Vacuum leak at the intake manifold gasket near cylinder 4, leaning out the mixture during start; Low compression on cylinder 4 due to worn piston rings or valve sealing problems; Faulty engine coolant temperature sensor causing an incorrect cold-start enrichment strategy

DTC codes / BMW codes / P1348

P1348 · BMWMisfire During Start Cylinder 4

Q: What does code P1348 mean?

Misfire During Start Cylinder 4. P1348 on BMW vehicles means the engine computer detected a misfire specifically on cylinder 4 during the engine start phase, before the engine reaches normal operating speed. The misfire is identified by crankshaft speed fluctuations immediately after cranking, which the DME (Digital Motor Electronics) compares against expected values for each cylinder.

P1348 on BMW vehicles means the engine computer detected a misfire specifically on cylinder 4 during the engine start phase, before the engine reaches normal operating speed. The misfire is identified by crankshaft speed fluctuations immediately after cranking, which the DME (Digital Motor Electronics) compares against expected values for each cylinder.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Rough or stumbling idle immediately after a cold start, often smoothing out once the engine warms up
A flashing or steady check engine light, sometimes accompanied by reduced engine power
Noticeable vibration or shaking from the engine bay during the first few seconds of running
Hard starting or extended cranking before the engine fires
Often no symptoms besides the warning light, especially if the misfire is intermittent

Common causes, most likely first

Worn or fouled spark plug on cylinder 4, especially common on turbocharged BMW engines with direct injection
Faulty ignition coil on cylinder 4, which often fails intermittently when cold
Leaking or clogged fuel injector on cylinder 4, causing an incorrect air-fuel mixture during start
Carbon buildup on intake valves, a known issue on BMW direct-injection engines that affects cold-start mixture quality
Vacuum leak at the intake manifold gasket near cylinder 4, leaning out the mixture during start
Low compression on cylinder 4 due to worn piston rings or valve sealing problems
Faulty engine coolant temperature sensor causing an incorrect cold-start enrichment strategy

How to diagnose and fix it

Scan all BMW-specific fault memory with a capable diagnostic tool and record freeze-frame data for P1348
Swap the ignition coil from cylinder 4 with a neighbouring cylinder and recheck whether the misfire follows the coil
Remove and inspect the spark plug on cylinder 4 for fouling, wear, or incorrect gap, and replace if needed
Perform a cold-start fuel trim and injector balance test to check for a leaking or clogged injector on cylinder 4
Check intake manifold gaskets and vacuum lines near cylinder 4 for leaks using a smoke tester
Run a compression test and, if low, a cylinder leak-down test on cylinder 4 to rule out mechanical faults
If carbon buildup is suspected, perform a walnut-blast intake valve cleaning procedure as BMW specifies

Cold-start misfires that hide when warm

A P1348 that only appears on the first start of the day and clears after warm-up is very often a failing ignition coil or a spark plug that breaks down under cold, rich conditions rather than a mechanical engine fault.
BMW direct-injection engines are prone to carbon accumulation on intake valves, and this can cause a start-specific misfire on one cylinder without setting a misfire code once the engine is running normally.
Technicians sometimes replace all coils and plugs when only cylinder 4 is flagged, but swapping the coil first is a cheap way to confirm whether the fault follows the component or stays with the cylinder.
A weak battery or slow cranking can cause the DME to misjudge crankshaft speed fluctuations and set a false P1348, so check battery voltage and cranking speed before condemning ignition parts.
Fuel injector problems on BMW direct-injection engines can be intermittent and temperature-dependent, so a cold-start injector balance test is more revealing than a static resistance check.

Can I keep driving with P1348?

You can usually drive the car short distances to a workshop, but avoid hard acceleration and long trips until the misfire is diagnosed, because unburned fuel can overheat the catalytic converter. If the check engine light flashes or the engine runs very rough, stop driving and arrange a tow.

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.