The HIS is connected to the transmission's oil circuit and supplies the automatic transmission's shift elements required for starting with oil. The HIS is an electromagnetically switchable spring-piston accumulator that fills up with oil while driving, tensioning a spring. These components are designed to modify a shift by essentially acting as a shock absorber for the fluid pressure that is applying a clutch, brake or band. Cushioning of this high pressure allows the apply component to engage gradually, instead of slamming on and rattling parts and bones alike. Second hand boxes are a minefield and the number of variations mind boggling and finding a suitable unit is hard enough in the UK never mind a colonial outpost, what is the VIN? If it is cracked, your electronics are FUBAR and fitting a used box with an unknown clutch very risky, we fit a new. Loss of power (gone into neutral), no gears can be selected, hydraulic pump runs constantly, you can see hydraulic fluid bubbling/rising out of the breather, flashing spanner icon where gear number usually shows. Within the DSG Mechatronic unit, the hydraulic pump pushes oil through the filter. The accumulator serves as a reservoir for the transmission fluid, which is vital for the proper functioning of the gearbox. But many people don't know how they work.