Mercedes-Benz M256

M256 Engine

The M256 is a 3.0-liter turbocharged inline-6 petrol engine that marked Mercedes-Benz's return to straight-six engines. Detailed with a 48V mild-hybrid system, it replaced the V6 M276. This engine is designed for smoothness and efficiency, incorporating an electric auxiliary compressor to eliminate turbo lag.

This overview summarizes the reliability of the Mercedes-Benz M256, including common issues and cost drivers.

Mercedes-Benz M256 engine — Image credit: Wikimedia Commons · CC BY-SA 4.0

Technical Specifications

Manufacturer

Mercedes-Benz

Fuel Type

Petrol

Displacement

3.0 L

Production

2017–Present

Power Output

367–435 hp

Emissions

Euro 6d

Reliability Analysis

The M256 is a highly sophisticated engine that delivers exceptional performance and refinement. With a risk score of 4.5/10, it is generally reliable, but its complexity introduces potential failure points, particularly with the 48V electrical system. Regular maintenance is essential, and buyers should verify the health of the hybrid components.

Common Problems & Weak Points

Issue	Typical Mileage	Repair Cost (Est.)	Severity
48V Starter-Generator Issues	~120,000 km	€2000 – €3500	High

48V Starter-Generator Issues

The M256 engine features a advanced 48-volt electrical system with an Integrated Starter-Generator (ISG). While generally reliable, failures of the ISG or related 48V components can occur. Symptoms include the vehicle failing to start or displaying critical electrical system warnings. Repairs can be expensive due to the complexity and cost of the parts, ranging from 2000 to 3500 Euros.

Typical Mileage: 120,000 km

Cost: €2000–3500

Buyer's Inspection Checklist

Check for any 48V battery or electrical system warning messages on the instrument cluster.
Listen for unusual noises during startup or idle, which could indicate ISG issues.
Verify that all software updates for the engine and hybrid system have been performed by a dealer.

Frequently Asked Questions

Is the M256 engine reliable?

The M256 has known weak points, but with good maintenance the reliability is solid. See the risk analysis and common problems for specifics. Start a report for a specific car.

How expensive are typical repairs?

Common repairs fall into a mid-range cost band depending on the issue and workshop. Check the cost ranges in the table. Use the used car report for specific listings.

Which model years are best for this engine?

Newer production years often include technical updates. Review the production years and revisions in the specs. Use Car Check for quick screening.

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