Volkswagen 01M / 01P

Volkswagen's transverse four-speed automatic — in the Golf Mk4 and the Transporter T4.

It is the gearbox the DSG replaced, and it has a poor reputation that is largely deserved and largely about heat: it was fitted to heavy vehicles, its cooling is marginal, and the fluid is what fails first.

Its characteristic failure is the valve body and the solenoids, producing a harsh or delayed engagement into drive, a flare on the 2–3 change, and eventually a limp mode locked in third. The limp mode reads as terminal and very often is not, which matters on cars of this age and value.

These were sold as filled for life and are not. A unit at 150,000 km on its original fill is the commonest version of every complaint above, and on this transmission a fluid and filter service is a diagnostic step rather than only maintenance.

The fluid is a specific VW specification, not a generic Dexron; using the wrong one produces exactly the harsh engagement it was meant to cure.