P0305 on BMW: How to Diagnose & Fix
Cylinder 5 Misfire Detected
7 BMW models · 7 documented issues · 1 critical · $180-$1,200 repair
P0305 on BMW by model: symptoms, diagnosis and fix
The N55 in the 335i is a direct-injection engine. Fuel is sprayed straight into the cylinders, so it never washes over the backs of the intake valves, and carbon builds up on them. Oil vapor that gets into the intake adds to the deposits. Over time the buildup restricts airflow and can cause rough idle, misfires, loss of power and lower fuel economy. FCP Euro notes the buildup on the N54 and N55 can get bad enough to almost close off the intake ports and valves.
Common Symptoms
- Rough idle
- Misfire codes
- Hesitation or loss of power
- Poor fuel economy
How to Fix
1. Confirm the cause first. A rough idle or misfire alone does not prove the valves need cleaning. Read the fault codes and rule out other causes such as ignition faults, fuel delivery problems and air leaks. If those check out, have the intake valves inspected to see whether the deposits are heavy enough to explain the problem. 2. If the valves are heavily coated, the repair is a walnut-shell blast cleaning. The intake manifold comes off, crushed walnut shell is blasted into each port to scrub the carbon off the valves, and a shop vacuum pulls out the media and debris. The cylinder head stays on. One shop replaces the OEM intake manifold gaskets as part of the job. BMWBlog says the cleaning is usually recommended around 60,000 miles. FCP Euro gives roughly 30,000-50,000 miles and says tuned engines may need it sooner. Cleaning will not fix a bad injector, an ignition fault or a worn part, so it only helps if carbon was the cause. 3. Cost: one independent BMW shop (Speed Logic) lists walnut blasting for the N54/N55/N20 at $300, including new OEM intake manifold gaskets. FCP Euro says a dealer can charge over $700. Prices vary by shop, so compare quotes that cover the same work. 4. Prevention: an oil catch can reduces the oil vapor that reaches the intake. It slows new buildup but does not remove carbon that is already there.
What you need to diagnose it
The repair instructions explicitly call for reading stored codes. Use a scanner that can read the named code families before choosing a repair.The recommended scanner supports these code families; confirm your exact year, model and module coverage before buying.
ANCEL AD310 Classic OBD-II Scanner
Read & clear engine (P) codes
$20–$40View
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Reading and clearing the code is DIY work. Module replacement or reprogramming is not — most modules are VIN-programmed, so a new one does nothing until a shop codes it to your car. Check for an open recall or service bulletin before buying anything.
Sources for this issue (4)
The B58 engine's valve cover gasket is prone to degradation and oil leaks, typically developing around 60,000-100,000 miles. The rubber gasket material shrinks and dries out through repeated heat cycles, allowing oil to seep and eventually drip down the sides of the engine. In more severe cases, oil can leak into the spark plug tubes, causing misfires and potential ignition coil damage.
Common Symptoms
- Burning oil smell from engine bay, especially after highway driving
- Visible oil seepage around valve cover edges
- Oil dripping on exhaust manifold causing smoke
- Oil pooling in spark plug wells causing misfires
- Low oil level between changes
How to Fix
Replace the valve cover gasket with an updated BMW part. If oil has entered spark plug tubes, replace spark plugs and inspect ignition coils. Clean all oil residue from the engine block. Some owners replace the entire valve cover assembly as the integrated PCV valve can also fail.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- FCP Euro Genuine BMW B58 valve-cover gasket service kit 11128621951KTOEM11128621951Cross-refKIT-11128621951KT
Fitment: 2017-2021 BMW M240i and M240i xDrive F22/F23 listed by FCP; confirm vehicle selection and inspect the complete cover before ordering.
- Elring B58 complete engine valve cover 11127645173OEM11127645173Cross-refELR-B34750
Fitment: 2017-2021 BMW M240i and M240i xDrive F22/F23 where vehicle selection confirms OE 11127645173.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
As a direct-injection engine, the B58 in the M340i does not have fuel washing over the intake valves, leading to gradual carbon deposit buildup on the valve backs. Oil vapors from the crankcase ventilation system deposit carbon that restricts airflow and reduces performance. Symptoms typically become noticeable after 50,000-80,000 miles, with rough idle, reduced throttle response, and minor misfires. The M340i's higher boost pressures can accelerate carbon accumulation compared to non-M B58 applications.
Common Symptoms
- Rough or uneven idle developing gradually
- Reduced throttle response and power
- Slight hesitation during acceleration from low RPM
- Minor misfires at idle, especially when cold
- Decreased fuel economy over time
How to Fix
Walnut blast the intake valves every 50,000-60,000 miles. This involves removing the intake manifold and blasting walnut shell media at the valve backs to remove carbon deposits. Some owners use catch cans to reduce oil vapor entering the intake. BMW's official position is that carbon buildup is normal for direct-injection engines.
Sources for this issue (1)
Like all S58-powered BMWs, the M4 CS's direct-injection-only fuel system means no fuel washes over the intake valves. Carbon deposits from crankcase ventilation oil vapors accumulate on the back of the intake valves over time, gradually restricting airflow. The M4 CS's aggressive driving profile and higher boost pressures may accelerate carbon accumulation. Symptoms typically develop gradually and become noticeable after 40,000-60,000 miles of driving.
Common Symptoms
- Progressive loss of power and throttle response
- Increasingly rough idle over months of driving
- Cold-start misfires that diminish once warmed up
- Decreased fuel economy compared to when new
- Slight hesitation during tip-in throttle at low RPM
How to Fix
Walnut blast the intake valves every 40,000-50,000 miles. Consider installing an oil catch can to reduce oil vapor ingestion. Maintain strict 5,000-7,000 mile oil change intervals with BMW LL-01 approved oil. Allow full engine warmup before spirited driving to ensure proper crankcase ventilation operation.
Sources for this issue (2)
Ignition coils on S63TU and S63B44T4 engines (F10 M5 2013-2016, F90 M5 2018-2023) fail far more frequently than on other BMW engines, with failures common before 30,000 miles. High-performance turbocharged nature of S63 creates extreme heat and electrical demands that stress ignition coils beyond their design limits. When one coil fails, it typically signals that other coils are nearing end of life. Failed coils cause misfires, rough running, and can damage catalytic converters if not addressed promptly. Owners on M5Board report that coil failure before 30,000 miles is common on S63 engines, so it is worth budgeting for. When one coil fails, M5Post members recommend replacing all 8 at once, since owners report the rest often fail within about 10,000 miles; this saves a second service visit and its labor cost.
Common Symptoms
- Engine misfires, especially under load or acceleration
- Rough idle and unstable engine operation
- Check engine light with misfire codes (P0300-P0308)
- Reduced power output
- Poor fuel economy
- Potential catalytic converter damage from unburned fuel
How to Fix
Replace failed ignition coil(s) immediately to prevent catalytic converter damage ($3,000-$5,000 additional). When one coil fails, M5Post recommends replacing all 8 coils as preventative maintenance ($600-$900 parts + labor) - they typically fail within a similar timeframe, and this saves a second service visit. Use OEM Bosch coils for best reliability ($50-$80 each) - aftermarket options fail even faster on S63 due to heat and electrical demands. Replace spark plugs simultaneously if mileage exceeds 30,000 miles ($280-$320 for 8 plugs). Labor: 1-2 hours. Single coil replacement: $179-$235.
Sources for this issue (1)
- BMW Ignition Coils for BMW 5 Series F10 (Turner Motorsport)parts-reference
The E89 Z4 sDrive35i and 35is use the N54 3.0L twin-turbo engine which has a well-documented high pressure fuel pump (HPFP) failure. The original HPFP used a split-design where fuel goes to one half and lubrication to the other, separated by an internal O-ring that degrades prematurely causing loss of fuel rail pressure. When the HPFP fails, the engine cannot maintain fuel pressure under boost, causing immediate loss of power, misfires, and potential engine stalling at highway speeds - a serious safety concern. BMW issued TSB SI B13 03 09 acknowledging the defect and released multiple revised pump versions. Early 2009 Z4 35i models are most affected. The HPFP went through multiple revision indexes, with the latest being the most reliable.
Common Symptoms
- Long cranking time before engine starts
- Engine stalling at idle or during acceleration
- Severe loss of power under boost (fuel pressure drops below 50 PSI)
- Rough idle and engine misfires (codes 29D0, 29D2, 29E2)
- Check engine light with fuel pressure fault codes
- Car enters limp mode with reduced power
- Fuel smell from engine bay due to injector overfueling at low pressure
How to Fix
Replace HPFP with latest revision Genuine BMW unit. The pump went through multiple revisions - ONLY install the latest version. Part number evolution: Original -> 13517592881 (Index 10, TSB fix) -> 13517616170 (latest revision, most reliable). Genuine BMW 13517616170 is the definitive fix ($350-$550 for pump). Replacement is straightforward DIY (1-2 hours) with basic tools. Also available as complete kit from FCP Euro with lifetime warranty. In the US, BMW extended HPFP warranty coverage to 10 years/120,000 miles, and MY2009-2010 Z4 sDrive35i were included in BMW's October 2010 N54 recall (pump replacement and/or software update) - check VIN eligibility. Replace low-pressure fuel sensor at same time (13537537319) as it may have been damaged by pressure fluctuations ($35-$55).
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine BMW exchange high-pressure fuel pump 13517616170OEM13517616170
Confirmed N54 high-pressure fuel-pump replacement. Fitment: 2009-2011 E89 Z4 sDrive35i and sDrive35is with N54 as cataloged; confirm VIN and rail-pressure diagnosis.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
P0305 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0305 mean on a BMW?
P0305 stands for "Cylinder 5 Misfire Detected." This code means the engine control module detected a misfire on cylinder number 5, meaning that cylinder is not burning its air-fuel mixture properly on some combustion cycles. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder fails to fire correctly. A misfire wastes fuel, can make the engine run rough or shake, and dumps unburned fuel into the exhaust, which can overheat and damage the catalytic converter. It generally points to a problem with spark, fuel delivery, or compression specifically affecting cylinder 5. On BMW it is documented across 7 models: 3 Series, M240i, M340i, M4 CS, M5, Z4, 1 Series.
What are the most common causes of P0305?
The most common causes of P0305 are: Worn or fouled spark plug on cylinder 5, Failed ignition coil or coil pack for cylinder 5, Faulty or clogged fuel injector on cylinder 5, Vacuum or intake air leak affecting that cylinder, Bad spark plug wire or boot (on applicable engines), Low compression from worn rings, valves, or head gasket, Carbon buildup or sticking valve on cylinder 5, Lean or rich fuel condition affecting the cylinder. The specific cause varies by vehicle.
How much does it cost to fix P0305 on a BMW?
Published repair estimates on BMW range from $180 to $1,200 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.