P0308 on BMW: How to Diagnose & Fix
Cylinder 8 Misfire Detected
2 BMW models · 2 documented issues · $180-$2,400 repair
P0308 on BMW by model: symptoms, diagnosis and fix
The N63's direct injectors sit in the hottest part of a hot-vee engine and fail early, either leaking down and washing the cylinder or losing flow entirely. The result is a persistent misfire isolated to one cylinder that follows the injector when you swap it to another bore - the diagnostic that separates an injector from a coil, plug, or HPFP problem. BMW went through several injector revisions and ran an index-level campaign, replacing early injectors with index 11 or higher on affected cars; checking the index number stamped on each injector is a standard step when diagnosing N63 misfires. Owners on BimmerFest report chasing a cylinder-specific misfire through coils, plugs and even swapped high-pressure fuel pumps before the injector proved to be the culprit.
Common Symptoms
- Rough idle
- Persistent misfire on one cylinder
- Check engine light flashing under load
- Fuel smell from the exhaust
- Reduced power / engine malfunction message
How to Fix
Read the misfire counters per cylinder, then swap the suspect injector to a different cylinder - if the misfire moves, the injector is bad. Check the injector index level; anything below the current index should be updated. Injectors must be coded to the DME with their calibration numbers after replacement, and BMW specifies new decoupling elements and Teflon seals. Many N63 injector replacements have been covered free of charge under BMW's extended injector program, with a 2-year warranty on the replaced parts even on out-of-warranty cars - ask the dealer before paying. Replace plugs at the same time since the washed cylinder has fouled them.
Sources for this issue (3)
Ignition coils on S63 and S63TU engines (F10 M5 2012-2016, 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. M5Board: ignition coil failure before 30k miles is NORMAL on S63 engines - budget for this, don't be shocked when dealer says "common issue." When one coil fails, M5Post recommends replacing all 8 at once since they'll all fail within 10k miles anyway - saves second service appointment and 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 similar timeframes and saves 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)
P0308 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 P0308 mean on a BMW?
P0308 stands for "Cylinder 8 Misfire Detected." P0308 means the engine computer detected a misfire on cylinder number 8 — that cylinder is failing to combust properly or at the correct time. The PCM identifies it by monitoring crankshaft speed variations as cylinder 8 fires. Misfires waste fuel, increase emissions, and can overheat and damage the catalytic converter, so a hard misfire may cause a flashing check engine light. Typical symptoms include rough idle, vibration, hesitation, and reduced power. On BMW it is documented across 2 models: 7 Series, M5.
What are the most common causes of P0308?
The most common causes of P0308 are: Worn, fouled, or incorrectly gapped spark plug on cylinder 8, Failed ignition coil or coil-on-plug for cylinder 8, Faulty, clogged, or leaking fuel injector, Vacuum or intake air leak affecting that cylinder, Low compression (worn rings, burnt/leaking valve, head gasket), Damaged spark plug wire or boot (on applicable engines), Carbon buildup or sticking valve. The specific cause varies by vehicle.
How much does it cost to fix P0308 on a BMW?
Published repair estimates on BMW range from $180 to $2,400 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.
Looking for P0308 on a different make?
View P0308 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.