Reconditioned BMW 1 Series Gearbox

Your 1 Series is a 2.0d: why the gearbox depends on the engine code, not the engine capacity

This is the most common pitfall with the 1 Series: two vehicles both badged "2.0d" can carry different gearboxes depending on whether the block is a M47D20 or a N47D20. These two codes correspond to two generations of 2.0 diesel engine that do not share the same gearbox pairings. The same logic applies to the 2.0d known as the 120d, which carries the code N47N and is a distinct variant in its own right. Engine capacity alone is not enough to select the correct reference.

Diesel, petrol, small blocks: a 6-speed manual gearbox but distinct references

The entire 1 Series range (2004–2019) is covered by 6-speed manual gearboxes, across both diesel and petrol engines. The diesels run from the 1.5d (B37C15A, B37D15A) and the 1.6d (N47D16A) through to the 2.0d in several block variants. On the petrol side, the 2.0i covers the codes N43B20 and N46B20 — two blocks of the same engine capacity but different design. The 3.0 and 3.0i all share the code N52B30, which simplifies identification for that segment.

Reading gearbox references on the 1 Series

BMW stamps a manufacturer reference of the type GS6-37DZ, GS6-45BZ or GS6-17DG on every gearbox — often followed by a multi-letter suffix that specifies the exact variant (e.g. GS6-45DZ-HAO, GS6-17DGSAAQ). These suffixes are not decorative: they distinguish different ratios, output configurations or engine compatibilities. Before placing any order, it is worth noting down the full reference stamped on the casing of the gearbox currently fitted, in addition to the engine code.