Mercedes-Benz M139
2.0 L · inline-4 · turbocharged · petrol · 2019–present
Also known as: m139, 2.0 amg four, a45 s engine, cla45 s engine, m139l
AMG's hand-built 2.0-litre four, and for years the most powerful production four-cylinder engine in the world — the successor to the M133, with the whole engine rotated so the turbocharger sits at the rear.
The number to keep in mind is specific output. It makes more than 175 hp per litre in standard form, and everything about its behaviour follows from that: boost pressure, charge temperature and oil condition are not maintenance details here, they are the operating envelope. A tired or incorrect oil, a marginal intercooler or an intake leak produces knock and heat-related faults far sooner than it would on an ordinary 2.0 turbo.
It is also among the most heavily modified engines on the road, so the standing question on any fault is what software and hardware the car is actually running. A knock or over-boost code on a modified M139 is usually reporting the modification rather than a component failure.
Cars fitted with this engine
7 generations, across 2 makes. From the authored catalogue — an absent car means the catalogue has not reached it, not that the engine was never fitted.
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Posted about this engine
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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