30FF Fault Code: Misfire on Multiple Cylinders (BMW Repair Guide)
30FF is a BMW-specific hex fault code stored by the DME when it detects combustion misfires on more than one cylinder. Its generic equivalent is P0300, and severity is high because of the risk of catalytic converter damage.
— Tekin Code
30FF is a code from BMW's own hex fault code system, stored by the DME, and it means "combustion misfire on multiple cylinders". You will see it most often on N54, N55, N20/N26, N13, N63 and B46/B48/B58 engines, typically after a cold start, at idle, or under full throttle. Severity is high: unburned fuel passes into the exhaust, so ignoring it can destroy the catalytic converter and turn a cheap job into a very expensive one.
What Does 30FF Mean?
The DME (Digital Motor Electronics) measures the crankshaft speed signal during every firing interval. When a cylinder fails to burn its charge, the crank momentarily slows down more than expected; the DME counts that deviation per cylinder as a "rough run" value. Once the counter crosses its threshold and the fault is not concentrated on a single cylinder, the DME logs 30FF.
30FF rarely shows up alone. If you also see cylinder-specific misfire codes in the 29CD–29D2 range, mixture codes (such as 2FBD or 2FBF) or fuel pressure codes, that is where the real clue is. On the generic OBD-II side this code corresponds to P0300 — most cheap ELM327 scanners will only show you P0300, which is exactly why reading the BMW protocol properly makes a difference.
Code .............. 30FF
Definition ........ Combustion misfire - multiple cylinders
Module ............ DME (Engine Control Unit)
Generic equivalent P0300
Related codes ..... 29CD-29D2 (per-cylinder misfire), 2FBD/2FBF (mixture)
Severity .......... High - catalytic converter at risk
Common engines .... N54, N55, N20/N26, N13, N63, B46/B48, B58
Symptoms
• Noticeable shaking at idle and unstable RPM — the engine feels like it is stumbling.
• Loss of power under acceleration, delayed throttle response, and in some cases limp mode.
• Check Engine / EML light on steady; if misfires are heavy, the light flashes.
• Hard cold start, strong shaking in the first 30–60 seconds, partially clearing up afterwards.
• Clearly higher fuel consumption and a raw fuel smell from the exhaust.
• On turbo engines: hesitation at full throttle, boost cut, or a stuttering feel.
• Vibration felt through the steering wheel and shifter at idle, getting worse with the A/C on.
Possible Causes
• Worn spark plugs — 25,000–40,000 miles on turbocharged BMW engines, sooner with hard driving. The most common cause by far.
• Failing ignition coils — several coils usually weaken in the same period, which is exactly why the fault is not limited to one cylinder.
• Vacuum leaks — torn PCV/CCV diaphragm, intake manifold gasket, cracked vacuum hoses.
• Charge air leaks — cracked charge pipe or a dislodged O-ring (especially the plastic charge pipe on N54/N55).
• Low fuel pressure — a weak HPFP, clogged fuel filter, or a tired low pressure pump.
• Leaking or wrongly indexed injectors — on direct injection engines the injector index must be coded after replacement.
• Carbon buildup on the intake valves — a classic direct injection issue past 50,000 miles that disturbs airflow.
• Dirty VANOS solenoids or a stretched timing chain causing incorrect valve timing.
• Weak battery or a missing AGM registration — low supply voltage directly reduces coil output.
• Poor quality fuel, water contamination, or octane that is too low.
• Mechanical causes — low compression, a burnt valve, or a head gasket issue (rarest, but the most expensive scenario).
Diagnostic Steps with OBDThink
The biggest mistake with 30FF is reading the code and immediately throwing plugs and coils at it. Because the code says "multiple cylinders", the root cause is usually something shared by all cylinders: air, fuel, or voltage. Work through the order without skipping steps.
• 1. Run a full scan: don't stop at the DME — scan all modules. If cylinder-specific codes (29CD–29D2) sit next to 30FF, note which cylinders dominate.
• 2. Read the freeze frame: RPM, engine load, coolant temperature and mileage at the moment of the fault tell you the scenario. Low temp + low load = a cold start problem; high load + high RPM = fuel pressure or weak coils.
• 3. Watch live data: at idle, monitor per-cylinder misfire counters, target vs. actual rail pressure, STFT and LTFT, the lambda signal and battery voltage together.
• 4. Interpret the fuel trims: if LTFT is clearly positive on both banks (above +10%), look for a vacuum/boost leak or low fuel pressure. If trims are normal, shift focus to the ignition side.
• 5. Swap test: move the coil from cylinder 1 to cylinder 4, clear the codes, and drive under the same conditions. If the misfire follows the coil, you found the culprit.
• 6. Check fuel pressure under load: if rail pressure drops well below target at full throttle, suspect the HPFP or the low pressure side.
• 7. Leak test: with high trims, smoke test the vacuum and charge air system; inspect the PCV diaphragm and the charge pipe.
• 8. Mechanical checks last: if everything above is clean, run a compression and leak-down test.
Idle reference values (engine warm, A/C off)
RPM ..................... 620 - 740 (fluctuation < +/- 40)
Rail pressure (high) .... 50 - 70 bar idle / 120 - 200 bar load
Low side pressure ....... 4.5 - 6.0 bar
STFT .................... -10% ... +10%
LTFT .................... -8% ... +8%
Lambda .................. ~1.00
Battery voltage (running) 13.8 - 14.6 V
Misfire counters ........ 0 on all cylinders
EXAMPLE OF A RED FLAG:
LTFT Bank1 +18% / Bank2 +17% -> shared cause: leak or fuel pressure
Misfire counters: Cyl2=41, Cyl5=38 -> ignition or injector side
With OBDThink you can log live data while driving. For an intermittent fault like 30FF, a PID recording from the exact moment the misfire happened tells you far more than watching the engine idle in a workshop.
The Fix
Work from the most likely cause to the rarest, based on what the diagnosis showed. Jumping straight to an expensive part is the single most common way people waste money on 30FF.
• Spark plugs: a full set of the correct heat range. Low cost, and on turbo engines they are usually due anyway at 25,000–40,000 miles. Replace as a set, not one at a time.
• Ignition coils: replace at least the coils on the affected cylinders, or the whole set on a high-mileage car. Low to moderate cost.
• PCV/CCV valve and vacuum hoses: a torn diaphragm is the classic reason for high LTFT. Moderate cost, labour varies by engine.
• Charge pipe and O-ring: cracked plastic charge pipes are very common on N54/N55; an aluminium replacement is the permanent fix. Low to moderate cost.
• Injectors: when replacing a leaking injector, the new injector's index number must be coded to the DME — skip that and the misfire stays. High cost.
• HPFP (high pressure fuel pump): replace once a pressure drop under load has been confirmed. High cost.
• Intake valve carbon cleaning (walnut blasting): past 60,000 miles on direct injection engines this fixes both the misfire and the sluggish response. Moderate to high cost.
• Battery and AGM/IBS registration: a new battery must always be registered, otherwise the charging strategy is wrong and low voltage triggers misfires. Low cost.
• Mechanical repair: if compression comes back low, valve/ring/gasket work is required. High cost.
If you fitted a new battery or replaced injectors, do not skip the coding step. Without AGM registration and injector index coding, 30FF usually comes back within days.
Can You Still Drive With This Code?
If the Check Engine light is FLASHING, stop driving. A flashing light means active, heavy misfire, and unburned fuel can melt the catalytic converter within minutes. If the light is steady and the car pulls normally, a short drive to the workshop is acceptable — but avoid high RPM, full throttle and long trips.
Clearing the code fixes nothing; it only resets the counters. The right approach is: do the repair, then clear the fault memory with OBDThink and repeat the same driving conditions (cold start, idle, full throttle acceleration) while watching the misfire counters live. If they stay at zero across several drive cycles, the problem is genuinely solved. If the code returns, compare the freeze frame — the conditions it returns under will point you to the one remaining suspect.