Volkswagen 01M transmission

The Volkswagen 01M transmission is an electronic/ hydraulic four-speed automatic transmission deployed in Cabrio, Jetta, Golf, GTI, New Beetle manufactured between 1995 through 2005, and transverse engine Passats manufactured between 1995 through 1997. This transmission was entirely engineered and most probably manufactured by the French company STA (owned by Renault) in Ruitz (Pas-de-Calais, France).

The 01M and its predecessor 096 are very similar to the other transmissions engineered and manufactured by STA: AR4, AD4 and AD8, which were deployed on Renault vehicles in the 1980s and 1990s. It is an electronically controlled transmission with a lockup torque converter, using planetary gears, clutch packs, and a gear-driven final drive with an open-differential. There is no chain inside this transmission. It does not have provision for a dipstick. It was determined that a dipstick and fill might invite owners to introduce incorrect or inferior fluid. More information on design and function can be found in VW's publications, mechanic's Self Study Programs SSP112 for early versions for the 92-94 096, or SSP172 for 01M from 95-06.

The transmission has an oil-to-liquid cooler mounted on top of the transmission. Transmission oil is heated/cooled by the engine antifreeze that runs through the cooler.

Some areas of failure on this transmission include damage to plastic internals due to fluid over-temperature conditions, internal fluid pressure leaks from torn piston diaphragms, worn piston bores for solenoids in aluminum valve body, and the resulting worn clutches and bands. Occasionally, the plastic speedometer drive gear will break and fall off of the differential carrier and the speedometer will stop working. To repair this, the transmission must be removed and the differential disassembled far enough to replace the plastic gear. With age, the resistance in the wiring and/or electrical terminals between the valve body and transmission controller can increase. The additional resistance may prevent the computer from reading the faint pulses from the transmission speed sensors. Any missing sensor signal causes the transmission to go to "fail safe" or "limpy" mode. This mode keeps the transmission in Third gear and the gear indicator in the instrument panel indicates all gears are selected simultaneously.

...
Wikipedia