BMW P0308: Cylinder 8 Misfire Detected — Diagnosis and Repair

P0308 means Cylinder 8 Misfire Detected. The DME records it when the crankshaft speed pattern identifies repeated combustion loss on cylinder 8; diagnosis must prove the named circuit or mechanism before parts are replaced. Use OBDThink to preserve the recording module and freeze frame for P0308, then test cylinder 8 ignition, injector, compression and mixture contribution in the condition that set the fault. What Does P0308 Mean? This standardized powertrain DTC concerns cylinder 8 ignition, injector, compression and mixture contribution. BMW component location and test routing vary by engine, chassis and DME software; use the VIN-specific wiring diagram and service plan. The code is not a parts verdict. Its defining evidence is that the crankshaft speed pattern identifies repeated combustion loss on cylinder 8, so compare command, actual response and electrical integrity in the same operating window. Code: P0308 Definition: Cylinder 8 Misfire Detected Module: DME (gasoline) or DDE where applicable Key evidence: the crankshaft speed pattern identifies repeated combustion loss on cylinder 8 Typical causes: a worn plug, weak coil, injector delivery error, intake leak at cylinder 8, low compression, coolant intrusion, or bank-specific mixture fault Severity: diagnose promptly Note: confirm engine and circuit variant by VIN First save the freeze frame. If the crankshaft speed pattern identifies repeated combustion loss on cylinder 8, test cylinder 8 ignition, injector, compression and mixture contribution before disconnecting parts or erasing the evidence. Symptoms • The characteristic pattern is a repeatable cylinder 8 shake under load, rising cylinder 8 counters, fuel smell and possible catalyst overheating. First save the freeze frame. If the crankshaft speed pattern identifies repeated combustion loss on cylinder 8, test cylinder 8 ignition, injector, compression and mixture contribution before disconnecting parts or erasing the evidence. • The freeze frame is most useful when it captures that the crankshaft speed pattern identifies repeated combustion loss on cylinder 8. • A graph of the affected channel beside its companion or target value exposes dropouts that a static scan misses. • Related faults should be sorted by time and module so a shared supply or mechanical cause is not mistaken for a second failure. Possible Causes Begin with accessible connections and supporting conditions, prove the component dynamically, and reserve expensive internal work for last. • Low cost: inspect terminal grip, contamination, strain and loom routing at cylinder 8 ignition, injector, compression and mixture contribution. • Low cost: verify the exact fuse, shared feed, ground, hose or oil path shown for the VIN instead of assuming a universal BMW layout. • Medium cost: dynamically test the named sensor, valve or actuator; decisive evidence is that the crankshaft speed pattern identifies repeated combustion loss on cylinder 8. • Medium cost: correct the verified system fault, with branches including a worn plug, weak coil, injector delivery error, intake leak at cylinder 8, low compression, coolant intrusion, or bank-specific mixture fault. • High cost: consider DME repair or internal mechanical work only after circuit loading, signal comparison and the VIN-specific BMW test plan agree. Diagnosis Steps with OBDThink OBDThink is an independent BMW coding and diagnostic mobile app and is not affiliated with BMW AG. Live data and freeze frame depth depend on the vehicle, adapter and module. • 1. Scan all modules with OBDThink; save P0308, the recording DME, status, frequency, companion faults and freeze frame before clearing. • 2. Recreate the stored condition safely and graph the affected signal against its target or redundant channel. Compare cylinder 8 rough-running data with the other cylinders, then use controlled coil/plug swaps, injector testing and compression or leak-down evidence. • 3. Inspect cylinder 8 ignition, injector, compression and mixture contribution; with power isolated where required, load-test supply and ground and check the signal dynamically rather than trusting continuity alone. • 4. Separate electrical from mechanical evidence by moving the harness while logging, then perform the relevant smoke, waveform, pressure, airflow, compression or oil-path test. • 5. After the proven repair, clear faults, repeat the relevant cold start or controlled drive cycle, and rescan every related module. IF the crankshaft speed pattern identifies repeated combustion loss on cylinder 8 AND the circuit load test fails -> repair the circuit ELSE IF the command is valid but the mechanism does not respond -> test cylinder 8 ignition, injector, compression and mixture contribution ELSE compare companion faults and the BMW VIN-specific test plan THEN clear, reproduce the condition, and rescan The fastest split is command versus response while testing cylinder 8 ignition, injector, compression and mixture contribution: a lost electrical load and a mechanically unresponsive part require different repairs. Repair • Low cost: reseat or repair the proven connector, terminal, wire, hose, ground, fuse path or oil-service error affecting cylinder 8 ignition, injector, compression and mixture contribution. Low cost: inspect terminal grip, contamination, strain and loom routing at cylinder 8 ignition, injector, compression and mixture contribution. • Medium cost: replace the confirmed sensor, valve, solenoid, coil, injector or actuator; perform only the adaptation specified for that VIN. Medium cost: dynamically test the named sensor, valve or actuator; decisive evidence is that the crankshaft speed pattern identifies repeated combustion loss on cylinder 8. • Medium cost: repair the demonstrated intake, EVAP, fuel, exhaust, airflow or oil-supply condition instead of masking its measurement. Medium cost: correct the verified system fault, with branches including a worn plug, weak coil, injector delivery error, intake leak at cylinder 8, low compression, coolant intrusion, or bank-specific mixture fault. • High cost: repair the DME, timing hardware, cylinder head, pump or internal engine only when BMW service-data tests exclude cheaper branches. The fastest split is command versus response while testing cylinder 8 ignition, injector, compression and mixture contribution: a lost electrical load and a mechanically unresponsive part require different repairs. After repair, verify that the crankshaft speed pattern identifies repeated combustion loss on cylinder 8 no longer occurs and that P0308 stays absent as pending and confirmed through the relevant monitor. Can You Drive with P0308? Stop for a flashing warning lamp, strong fuel smell or severe shaking because unburned fuel can overheat the catalyst. Treat P0308 as measured evidence. The saved operating condition, target-to-actual comparison and loaded circuit test identify the least costly defensible repair.