Too Much

• An excessive amount of transmission fluid can negatively affect a transmission. When fluid levels are too great, it can result in air mixing in with the transmission fluid. This can cause slipping in a transmission as well as other gear-shifting issues.
  
  

Too Little

• When transmission fluid levels are too low, this can also be damaging to a transmission. It can slip or be slow to engage when not enough fluid has been added. Keep the fluid levels between the Full and Add section of your transmission's dipstick.
  
  

Check Levels

• Because a transmission should be hot when performing fluid level checks, a vehicle should be put in park and left idling during this process. If everything is fine, you won't get a low-level fluid reading because transmissions don't consume fluid during operation. A low level reading often indicates a leak.