ZF 4HP20

ZF's transverse four-speed — in the Peugeot 307 and 407.

It is not the AL4/DP0, PSA's own four-speed that appears in the same cars in the same years. The two are routinely conflated, including in parts listings, and they share neither internals nor fluid — so the first question about a four-speed automatic Peugeot is which of the two is fitted.

Nor is it the 4HP22, ZF's longitudinal four-speed of nearly the same name in Land Rovers and BMWs. Three gearboxes, two of them ZF's own, and a naming scheme that separates them by one digit.

Its recurring failure is the valve body and the solenoids, presenting as a harsh or delayed engagement and a change that arrives late. The fluid specification is ZF's and not a generic Dexron, and on a car of this age the fluid's history is unknowable and usually poor — which is why a service comes before a diagnosis rather than after one.