Mercedes engine codes begin with either OM (diesel) or M (petrol). This guide explains the difference, lists the most common OM and M series engines, and shows you exactly how to identify which engine is in your car.
Mercedes engine codes starting with OM are diesel engines; those starting with M are petrol. OM stands for Öl-Motor (oil engine) and M for Motor. The most common OM diesel is the OM651 (2.1‑litre, 1,250 enquiries in 2025 [EM‑VERIFIED]), while the most common M petrol is the M276 (3.0‑litre V6, 390 enquiries [EM‑VERIFIED]).
Use the full matrix below to see which OM or M engine fits your chassis, then confirm with our VIN decoder.
This table lists the most common OM and M engine families, their fuel type, displacement, chassis codes, and 2025 enquiry volumes. Use it to see which engines are fitted to which Mercedes models.
| Engine Code | Fuel | Displacement | Chassis Codes | Key Models | EM Requests 2025 |
|---|---|---|---|---|---|
| OM651 | Diesel | 2.1 L | W204, W205, W212, W213, X253, W447, W906 | C‑Class, E‑Class, GLC, Sprinter | 1,250 [EM‑VERIFIED] |
| OM654 | Diesel | 2.0 L | W205, W206, W213, W214, X253, X254, V167 | C‑Class, E‑Class, GLC, GLE | 520 [EM‑VERIFIED] |
| OM642 | Diesel | 3.0 V6 | W211, W212, W164, W166, X204, W251, W906 | E‑Class, ML/GLE, GLK, Sprinter | 880 [EM‑VERIFIED] |
| OM646 | Diesel | 2.1 L | W204, W211, W906 | C‑Class, E‑Class, Sprinter (pre‑2010) | Not in top 62 |
| OM656 | Diesel | 2.9 L | W213, W222, W223, V167 | E‑Class, S‑Class, GLE | Not in top 62 |
| M276 | Petrol | 3.0 V6 | W212, W213, W166, C218, X166 | E‑Class, CLS, GLE, GLS | 390 [EM‑VERIFIED] |
| M274 | Petrol | 2.0 L | W205, W213, X253 | C‑Class, E‑Class, GLC | Not in top 62 |
| M272 | Petrol | 3.5 V6 | W203, W204, W211, W164, X204, C219, R171, W221 (early) | C‑Class, E‑Class, ML, GLK, CLS, SLK, S‑Class | Not in top 62 |
| M270 | Petrol | 2.0 L | W176, W246, X156 | A‑Class, B‑Class, GLA | Not in top 62 |
| M177 | Petrol | 4.0 V8 Biturbo | W205, W213, W222, X166, V167 | C63, E63, S‑Class, GLE/GLS AMG | 370 [EM‑VERIFIED] |
| M157 | Petrol | 5.5 V8 Biturbo | W212, W221, W222, X166, C218 | E63, S63, GLE63, CLS63 | Not in top 62 |
| M156 | Petrol | 6.2 V8 | W204, W212, X164, W463 | C63, E63, ML63, G63 | Not in top 62 |
For a complete list of all engines, visit the full fitment matrix. For side‑by‑side comparisons, see M272 vs M276 and OM642 vs OM651.
Use these three methods to confirm whether you have an OM diesel or an M petrol engine.
Open the bonnet and locate the sticker on the timing cover or camshaft cover. The code will start with OM or M – for example, OM651 or M276. This is the most direct method.
The 8th character of your VIN often indicates the engine family. Use our free Mercedes VIN decoder for a full breakdown, including the exact engine code.
The engine number is listed on the registration document; the code is usually the first part of that number. Cross‑reference with our Engine Code Guide.
If you cannot locate the code, a vetted Mercedes specialist can identify it during a service.
Installing the wrong engine type (OM diesel in an M petrol chassis or vice versa) is one of the most expensive mistakes you can make. Here's why getting the fuel type right is critical:
Once you've confirmed the engine, you can check replacement costs and use the repair vs. replace calculator to make an informed decision.
Even experienced owners sometimes confuse diesel and petrol codes. Avoid these common mistakes:
If you are still unsure, use the full fitment matrix or contact a specialist.
The easiest way is to check the 8th character of your VIN. Use our VIN decoder to get a full breakdown. You can also look at the fuel filler cap – diesel will have a "Diesel" label, petrol will be "Super" or "Premium". But for the exact engine code, the VIN or logbook is most reliable.
"OM" stands for Öl-Motor, which is German for oil engine – i.e., diesel. "M" stands for Motor and is used for petrol engines. This naming convention has been in place for decades.
No – the engine mounts, ECU, wiring, fuel system, and exhaust are all different. It is not a practical DIY swap and would cost more than simply replacing with the correct engine. Always replace like‑for‑like.
It depends on the specific engine. Generally, the newer OM654 diesel is considered more reliable than the older OM651. Among petrol, the M276 is more reliable than the M272 (which has a balance‑shaft issue). For detailed verdicts, see each engine's Knowledge Centre.
Supply‑only costs vary. A reconditioned OM651 is around £2,800–£4,800, an OM642 is £3,200–£5,500, and an M276 is £3,800–£6,500 [EM‑QUOTE]. Labour for R&R is typically 12–16 hours, adding £780–£1,040 at independent rates. See the replacement cost guide for full details.
If the cost of a replacement engine (supply + fitting) exceeds approximately 70% of your car's current market value, it may be more economical to scrap the car. For an older OM651 in a W204 C‑Class, the threshold is often reached; for a newer M276 in a W213 E‑Class, replacement is usually viable. See the repair/replace/scrap framework for worked examples.
Knowing whether your Mercedes has an OM diesel or M petrol engine is the first and most important step before any engine work. Use the methods above – engine code label, VIN decoder, or V5C – to confirm the fuel type and exact engine code.
Once identified, you can assess the repair or replacement cost. If your engine has failed, compare the reconditioned cost against your vehicle's value using the repair vs. replace calculator. Always use a vetted Mercedes specialist for the work.
Check Your Engine with Registration LookupReady to identify your engine or get a quote? Compare prices from vetted Mercedes specialists.