Mercedes M254 Engine: Engine Number, Mild Hybrid & Replacement

The Mercedes M254 engine is a turbocharged inline four-cylinder petrol engine that Mercedes-Benz builds with 1.5 and 2.0 litres of displacement. Its hallmark is the integrated starter generator (ISG) on a 48-volt electrical system, in other words a mild-hybrid setup. If you are looking for a used or replacement M254, the first thing you need is the exact engine number, for example 254.920.

What is the Mercedes M254 engine?

The M254 belongs to the current generation of Mercedes four-cylinder engines and was designed for electrification from the start. Mercedes first introduced it in the facelifted E-Class, and it then became the petrol engine of the 206-series C-Class. Compared with older four-cylinders it has a few technical features worth knowing:

• Four cylinders in line, turbocharged petrol engine with 1.5 or 2.0 litres
• Second-generation integrated starter generator (ISG) on a 48-volt system, adding around 15 kW for short bursts under acceleration and recovering energy when braking
• Depending on the version, an electric auxiliary compressor that builds boost quickly at low engine speeds
• NANOSLIDE coating on the cylinder bores
• Exhaust aftertreatment mounted close to the engine

One point matters when you replace the engine: the second-generation ISG is no longer part of the engine but part of the transmission. It sits between engine and gearbox and is built into the gearbox side. So when you order an M254, check exactly which parts come with the engine and what stays with the gearbox.

Engine number and series: reading 254.920

On a Mercedes, the engine number is stamped into the engine block. The first three digits give the engine series: 254 means M254. The digits after the dot identify the exact version. In our listings you will find the number without the dot, for example 254920.

The series alone is not enough. Under the “M254” name there are different displacements, power outputs and versions for mild hybrids and plug-in hybrids. Ancillaries, wiring and software can differ. So rely on the full engine number and, where available, the OE number. Our guide on finding your engine code explains where to look.

Which models use the M254?

The M254 is the four-cylinder petrol engine of the current Mercedes mid-size range. It is used in, among others, the C-Class (206 series), the E-Class and the GLC, both as a mild hybrid and in plug-in hybrids such as the C 300 e. The model badge tells you little about the exact version: the same model name does not automatically mean the same engine number.

Our own stock shows how widely one engine version is used. We have had engines with number 254920 from vehicles such as:

• C-Class W206: C 300 e and C 400 e
• E-Class W214: including E 200, E 300 and E 300 e
• GLC: including GLC 200, GLC 300 and GLC 300 e

All engines of this series currently available are listed under Mercedes M254 engines; other series are under Mercedes-Benz engines. Stock changes all the time, so it is worth checking back.

Mercedes M254 engine: known weak points?

The M254 is a relatively young engine. Unlike some older engine series, there are so far no weak points that are widely and consistently described in the trade. Individual owner reports exist, but they do not add up to a general pattern. That is why we deliberately do not list typical faults here.

For diagnosis and buying, the usual rules for any modern turbo petrol engine still apply:

• Oil level and oil changes: the service history shows how well the engine has been looked after.
• Cooling system: overheating is a common cause of serious engine damage on any engine.
• Cause of the failure: find out why the old engine failed before the replacement goes in.
• Hybrid components: a fault in the 48-volt system or the ISG is not automatically an engine failure. Proper diagnosis avoids unnecessary costs.

What to check on a used M254

1. Compare the engine number: the number on your engine block and the number in the listing should match. If the OE number matches as well, you are on safe ground.
2. Mild hybrid or plug-in hybrid: check which vehicle the engine came from. The listing title names the donor model, such as C 300 e or E 200.
3. Mileage and condition: mileage and condition (new, used or remanufactured) are stated on every listing. The warranty is 12 months on used and remanufactured engines and 24 months on new parts (0 km), with no mileage limit.
4. Completeness and ancillaries: read the description to see which ancillaries are included. Pay particular attention to the hybrid components: because the ISG belongs to the gearbox, agree in advance what will be transferred from the old drivetrain.
5. Professional fitting: have the engine fitted by a workshop and follow the manufacturer’s instructions, such as changing the oil, bleeding the cooling system and checking the timing drive. Work on the 48-volt or high-voltage system belongs in qualified hands. That way the warranty stays fully valid. See our engine replacement checklist.

A core deposit applies when you buy an engine, usually €500. The exact amount is shown on the listing and added to your basket automatically. Return the identical, complete old engine, ideally handed to the haulier on the same pallet, and you get the deposit back in full after inspection. More in core deposit explained.

Need help finding your M254?

Not sure which M254 version is in your car, or is the engine number hard to read? Call us on +49 4950 93890 (Mon–Fri 8:30–12:30 and 13:30–17:30) or email info@motoren-dejong.de. Please have your VIN to hand. Or browse our overview of M254 engines.