P0300 on Mercedes-Benz: How to Diagnose & Fix
Random/Multiple Cylinder Misfire Detected
3 Mercedes-Benz models · 6 documented issues · 4 critical · $300-$20,000 repair
P0300 on Mercedes-Benz by model: symptoms, diagnosis and fix
Like other Mercedes direct-injected turbo engines, the M260 in the GLB (and the 1.3L M282 in the GLB 180/200) accumulates carbon deposits on the intake valves and intake tract over time because fuel is injected directly into the cylinder and never washes the back of the valves. This leads to unstable idle, hesitation, reduced power and worse fuel economy as mileage climbs, and German sources note the 1.3L can also develop coked injectors. It is a wear/maintenance issue, not a recall.
Common Symptoms
- Unstable / rough idle
- Hesitation on acceleration
- Loss of power
- Reduced fuel economy
- Cold-start stumble
How to Fix
Periodic walnut-blasting / intake valve cleaning resolves the deposits; some owners use quality top-tier fuel and occasional intake cleaners as mitigation. Keeping up with oil changes using MB-approved oil reduces oil-vapor contribution from the PCV system. Walnut-blast cleaning typically costs roughly 300-600 USD depending on shop.
Sources for this issue (2)
Mercedes-Benz extended the exhaust-valve-system warranty to 15 years or 150,000 miles for certain model-year 2020-2022 GLB 250, GLB 250 4MATIC and AMG GLB 35 vehicles. The notice identifies valve-guide and/or seat-ring wear from increased lateral forces, which can cause cylinder misfires and an illuminated malfunction indicator lamp. Manufacturer communication 11028267 separately identifies a leaking valve seat, requires cylinder leakage testing and calls for complete cylinder-head replacement only when valve-seat damage is confirmed. Coverage and parts are VIN-specific; neither document establishes a universal manufacturing defect, owner-frequency rate or automatic cylinder-head replacement.
Common Symptoms
- misfire and mixture faults preserved
- cylinder leakage measured and located
- VIN checked for extended-warranty coverage
How to Fix
Preserve codes and perform the Mercedes cylinder-leakage procedure to identify whether leakage is at an intake or exhaust valve. Check the VIN in NetStar/VMI for extended-warranty coverage. Replace the complete cylinder head only if valve-seat damage is confirmed under the applicable procedure. Do not buy a cylinder head, valves, guides or timing parts from this page; coverage and parts must be determined by VIN.
Sources for this issue (2)
The 4.0L biturbo M177 V8 in the W463A G 550 and AMG G 63 is documented for above-normal engine oil consumption (often 1 quart per ~1,000-2,000 miles in worse cases), with the most severe outcome being cylinder bore/liner scoring and piston ring wear at higher mileage. The high-output, hot-running twin-turbo design stresses piston rings and the iron-coated aluminum bores; carbon buildup and ring coking aggravate consumption. If left unaddressed, low oil level can lead to bearing/piston damage. Owners report repeated low-oil warnings between services and, in advanced cases, misfires and blue exhaust smoke.
Common Symptoms
- Frequent low oil level warnings
- Oil consumption between services
- Blue/grey exhaust smoke
- Misfire at higher mileage
- Rough idle
How to Fix
Check oil level frequently and top up with the correct MB 229.5/AMG-spec full-synthetic oil; do not rely solely on service intervals. Diagnose with an oil-consumption test and leak-down/compression test; rule out the common contributors first (PCV/oil separator diaphragm, valve seals, turbo seals). Walnut-blast intake valves if carbon-fouled. Confirmed cylinder scoring requires a short block or engine replacement, ideally under powertrain warranty.
Sources for this issue (3)
The 5.5L M157 biturbo V8 used in the W463 AMG G 63 before the 2019 redesign is documented for cylinder wall scoring/scuffing at higher mileage plus weaknesses in timing-chain components and camshaft (VVT) adjusters. The camshaft adjuster magnets/solenoids meter oil to the VVT and chain; restricted flow accelerates chain and gear wear. Oil intrusion into the camshaft position sensor wiring can also mimic internal engine faults. Symptoms range from multi-cylinder misfires to rattle and, in worst cases, metal in the oil from bore scoring.
Common Symptoms
- Multi-cylinder misfire
- Engine rattle/timing noise
- Rough running
- Check engine light
- Metal particles in oil (advanced)
How to Fix
Use only the correct AMG-spec synthetic oil and shorter change intervals. Diagnose misfires by checking camshaft adjusters/solenoids and cleaning oil-contaminated sensor connectors before assuming internal failure. Inspect timing chain, tensioner and sprockets; replace worn camshaft adjusters. Confirmed cylinder scoring requires major engine work or replacement.
Sources for this issue (3)
The 1.3L turbocharged direct-injection M282 engine (co-developed with Renault, used in A180/A200) suffers carbon deposit buildup on the intake valves and ports because direct injection does not wash the valve backs with fuel. On urban/short-trip duty cycles deposits accumulate from roughly 60,000 miles, causing rough running and hesitation.
Common Symptoms
- Rough idle
- Hesitation at 1500-2500 rpm
- Reduced fuel economy
- Flat/sluggish acceleration
- Misfire under load
How to Fix
Walnut-shell media blasting of the intake valves/ports, typically recommended every ~50,000-60,000 miles. Using top-tier fuel, periodic intake/induction cleaning, and avoiding constant short trips slows buildup. A quality oil meeting the MB spec helps limit blow-by contribution.
Sources for this issue (2)
On the M260 2.0L four-cylinder turbo used in the A220, A250 and A35 AMG (and the CLA250, GLA250, GLB250), the exhaust valve seat rings and valve guides can wear prematurely so that the exhaust valves no longer seal. The result is a loss of compression on one or more cylinders, rough idle and misfire codes, and in advanced cases a rattling/ticking top end. Mercedes-Benz USA acknowledged the defect in August 2023 with an Emission Warranty Extension (document MC-10241534-0001, TSB 'ELW-ExhaustValve') covering 2019-2022 A-Class, CLA, GLA and GLB with the M260, extending coverage on the exhaust valve system to 15 years/150,000 miles. Owners on MBWorld and A-Class Club report dealers replacing the complete cylinder head under the extension, and UK A35 owners have documented loss-of-compression diagnoses on the same engine. This is separate from the M282 1.3L intake carbon issue: the M282 is a different (Renault co-developed) engine and does not share this valve-seat defect.
Common Symptoms
- Rough idle and misfire, especially cold
- Check engine light with cylinder misfire codes
- Low compression on one or more cylinders in a leak-down test
- Loss of power, hesitation under load
- Ticking or rattling noise from the cylinder head
How to Fix
Free repair within 15 years/150,000 miles for US 2019-2022 cars under the MBUSA exhaust-valve warranty extension: the dealer performs a leak-down/compression test and replaces the cylinder head assembly (valves, seats, guides) as needed; owners who paid for this repair before the extension can claim reimbursement with documentation. Outside the US or outside the extension, a replacement cylinder head on the M260 is a $4,000-$7,000 job, so any persistent P0300-P0304 misfire on a low-mileage M260 should be compression-tested before spending money on plugs and coils.
Sources for this issue (5)
- Mercedes-Benz Emission Warranty Extension MC-10241534-0001 (exhaust valve system, 15 yr/150,000 mi)tsb
- Warranty Repair - Cylinder Head! - MBWorld.org (GLB250, M260)forum
- Cylinder Head Extended Warranty M260 Engine - A-Class Clubforum
- A35 AMG loss of compression - MBClub UKforum
- 2019 Mercedes-Benz A220 TSBs (incl. ELW-ExhaustValve, Aug 3 2023)tsb
P0300 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 P0300 mean on a Mercedes-Benz?
P0300 stands for "Random/Multiple Cylinder Misfire Detected." P0300 means the engine computer detected misfires occurring randomly or across multiple cylinders rather than in one specific cylinder. A misfire is when a cylinder fails to ignite its fuel-air mixture properly, which the computer senses through small fluctuations in crankshaft speed. Because it's not isolated to one cylinder, the cause is usually something that affects the whole engine — like fuel, air, or ignition system problems — rather than a single coil or plug. Persistent or heavy misfiring wastes fuel, runs rough, and can damage the catalytic converter, which is why a flashing check engine light should be taken seriously. On Mercedes-Benz it is documented across 3 models: GLB, G-Class, A-Class.
What are the most common causes of P0300?
The most common causes of P0300 are: Worn or fouled spark plugs (across cylinders), Vacuum or intake air leak, Weak fuel pump, clogged fuel filter, or low fuel pressure, Failing ignition coils or worn spark plug wires, Dirty or faulty mass airflow (MAF) sensor, Clogged or dirty fuel injectors, Faulty crankshaft/camshaft position sensor, Low compression or EGR/PCV system faults. The specific cause varies by vehicle.
How much does it cost to fix P0300 on a Mercedes-Benz?
Published repair estimates on Mercedes-Benz range from $300 to $20,000 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 P0300 on a different make?
View P0300 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.