BMW 2F00 — Cylinder 2 Misfire
P0302 · Misfire detected
Cylinder-specific misfire codes indicate the DME has detected irregular combustion events on an individual cylinder through crankshaft speed variation monitoring. Fault code 2F00 identifies cylinder 2 as the misfiring cylinder. BMW uses a firing-order-based cylinder numbering system — cylinder 2's physical location depends on the engine configuration (inline-4, inline-6, V8).
The DME detects misfires by monitoring crankshaft rotational speed variations through the crankshaft position sensor. When a cylinder fails to produce its expected power contribution, the crankshaft decelerates slightly during that cylinder's power stroke. The DME counts these events and, if the misfire rate exceeds calibrated thresholds, stores a cylinder-specific fault code.
Safety warning
Persistent misfires can damage the catalytic converter by sending unburned fuel into the exhaust system. If the MIL is flashing (not steady), catalytic converter damage is occurring in real time — reduce engine load immediately and address the fault before further driving.
- Module
- DME
- Severity
- Warning
Symptoms
- Rough idle, especially noticeable at cold start
- Engine vibration or shaking at idle or low RPM
- Hesitation or stumble during acceleration
- Check engine light illuminated (steady = misfire detected; flashing = active catalyst-damaging misfire)
- Possible fuel smell from unburned fuel exiting through the exhaust
- Reduced engine power and poor fuel economy
Common causes
- Failed or worn spark plug on cylinder 2 (most common — BMW specifies replacement intervals that are often exceeded)
- Failed ignition coil on cylinder 2
- Faulty or clogged fuel injector on cylinder 2
- Vacuum leak at the intake manifold gasket or runner seal near cylinder 2
- Low compression on cylinder 2 (worn valve seals, damaged piston rings, or carbon buildup on valves — particularly common on N54/N55 direct-injection engines)
- Faulty crankshaft or camshaft position sensor (can cause phantom misfire codes, but typically sets additional sensor-specific faults)
Diagnosis
Identify cylinder 2's physical location. On BMW inline-6 engines, cylinders are numbered 1–6 front to rear. Cylinder 2 is the second from the front of the engine. On inline-4 engines (N20, B48), cylinder 2 is also second from front. On V8 engines (N62, N63), consult the engine-specific cylinder layout — bank and cylinder numbering varies.
Swap the ignition coil. Move the ignition coil from cylinder 2 to another cylinder (e.g., cylinder 4) and vice versa. Clear faults and run the engine. If the misfire follows the coil (now showing on cylinder 4), the coil is faulty — replace it.
Swap the spark plug. If the misfire stayed on cylinder 2 after the coil swap, perform the same swap test with the spark plug. Inspect the removed plug for electrode wear, carbon fouling, oil fouling, or physical damage. Replace spark plugs as a set if they are beyond their service interval.
Test the fuel injector. Using ISTA or INPA, run the injector cutoff test (Zylindergleichtest / relative compression test). This test sequentially disables each injector and compares the RPM drop. A cylinder that shows little or no RPM change when its injector is cut was already not contributing — confirming the misfire. To isolate the injector specifically, swap it with an adjacent cylinder and retest.
Check for vacuum leaks. Inspect the intake manifold gasket and individual runner seals near cylinder 2. Use a smoke machine or carb cleaner spray method — an RPM change when spraying near a gasket indicates a leak. On N54 engines, the charge pipe and intercooler couplings are also common leak points.
Perform a compression test or leak-down test. If ignition, fuel, and air supply checks pass, test cylinder 2 for mechanical integrity. Compression should be within 10% of the other cylinders. A low reading suggests valve seal issues, ring wear, or carbon deposits on intake valves (direct-injection engines).
Inspect intake valves (direct-injection engines). On N54, N55, N20, and B-series engines, carbon buildup on the intake valves is a known issue. An endoscope inspection through the intake runner can confirm heavy carbon deposits restricting airflow and valve sealing.
Resolution
- Faulty ignition coil: Replace the coil. Consider replacing all coils as a set if they are original and high-mileage.
- Worn spark plugs: Replace all spark plugs as a set with BMW-specified plugs at the correct gap. Consult BMW ETK / RealOEM for your VIN.
- Clogged injector: Professional ultrasonic cleaning or replacement. Injectors should be replaced as a set if one has failed.
- Vacuum leak: Replace the failed gasket or seal. On N54 charge pipes, upgraded aluminum replacements are available.
- Low compression / carbon buildup: Walnut shell blasting of intake valves for carbon deposits. Mechanical engine repair for ring or valve seal issues.
- Clear fault codes after repair and verify no misfire recurrence over several drive cycles.