Automatic transmission fluid is used in conventional automatics, CVT units, dual-clutch transmissions, power steering systems and some hydraulic applications.

ATF is not a general purpose oil. Alongside viscosity and anti-wear protection it has to deliver a precise friction characteristic so clutch packs and torque converter lock-up engage smoothly and hold without shudder. That requirement differs between transmission families, which is why the wrong ATF causes harsh shifts, slipping or long-term clutch damage even though the fluid looks identical in the bottle.

Older units generally take a Dexron or Mercon type fluid, while modern six, eight and nine-speed automatics and CVTs each specify their own. Check the handbook or transmission plate before topping up, and treat multi-vehicle fluids as suitable only where they explicitly list your specification.