P0304 on Mercedes-Benz
Cylinder 4 Misfire Detected
P0304 on Mercedes-Benz vehicles indicates cylinder 4 misfire detected. Au7o has documented this code across 1 Mercedes-Benz model — most commonly on GLB. This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression.
Common Causes of P0304
- •Worn or fouled spark plug in cylinder 4
- •Failed or weak ignition coil on cylinder 4
- •Faulty spark plug wire or boot (where applicable)
- •Clogged, stuck or leaking fuel injector for cylinder 4
- •Vacuum or intake air leak near that cylinder
- •Low compression (worn rings, burnt/leaking valve, head gasket)
- •Damaged wiring or connector at the coil or injector
P0304 on Mercedes-Benz by Model
Mercedes-Benz GLB(1 issue)
- M260 Cylinder Head Exhaust Valve Seat/Guide Wear (Misfires, Compression Loss)2020-2022
The 2.0L turbo M260 four-cylinder used in the GLB 250 / GLB 35 (and the M264-related variants) suffers from premature wear of the exhaust valve seats and valve guides. The exhaust valves stop sealing, causing loss of compression in one or more cylinders, rough running and misfires. Mercedes acknowledged this as a manufacturing defect and issued a voluntary extended warranty in the US and Canada covering cylinder head replacement for up to 15 years / 150,000 miles on affected 2019-2022 A-Class, CLA, GLA and GLB vehicles. A 2026 NHTSA-posted TSB (MC-11028267) documents the valve seat/guide wear on M260/M264 engines. Left unaddressed it can progress to catastrophic piston/secondary damage that is NOT covered by the warranty extension.
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View P0304 across all makes →Frequently Asked Questions
What does P0304 mean on Mercedes-Benz?▼
P0304 stands for "Cylinder 4 Misfire Detected." This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression. On Mercedes-Benz specifically, this code is documented across 1 model.
What causes P0304 on Mercedes-Benz vehicles?▼
Common causes on Mercedes-Benz: Worn or fouled spark plug in cylinder 4, Failed or weak ignition coil on cylinder 4, Faulty spark plug wire or boot (where applicable), Clogged, stuck or leaking fuel injector for cylinder 4, Vacuum or intake air leak near that cylinder. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0304 on a Mercedes-Benz?▼
Repair costs vary widely depending on the root cause and specific Mercedes-Benz model.
Which Mercedes-Benz models have P0304 documented?▼
Au7o has documented P0304 on 1 Mercedes-Benz model: GLB.