Also known as: m54b25, m54b30, m54b22, 2.5i, 330i engine, e46 six
The straight-six of the E46 and E39 era, in 2.2, 2.5 and 3.0 litre forms — an iron-block, port-injected, double-VANOS engine from the period many owners consider BMW's most straightforward, and the reason those cars remain serviceable.
Its characteristic fault is a vacuum leak, and that matters because of what the leak looks like on a scan tool. The intake boot, the crankcase ventilation system and the various vacuum lines all harden with age; the result is lean-mixture codes on one or both banks, a hunting idle, and a fuel-trim picture that points at the oxygen sensors. Replacing sensors on an M54 with lean codes is one of the classic wasted repairs — test for unmetered air first.
The crankcase ventilation valve is the specific part worth naming, because in cold climates it freezes and the resulting crankcase pressure pushes oil past the seals. The double-VANOS units also wear, producing rough running and timing codes that read as camshaft-position faults.
Cars fitted with this engine
8 generations, across 1 make. 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.
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