TSB out on this
There is a tech service bulletin officially out on this and a fix was made for certain years of Runners. Some debate as to whether or not the repair really improves the symptoms, i.e. gas gauge reads much lower than what is actually left in the tank.
Search here or Yota Tech under "gas gauge" or some such verbage. Probably the most common complaint on the 3rd gen Runners.
Simple fix is to just learn thatwhen the light comes on you will be needing gas within 3-5 gallons. Fill up early or takes your chances by watching your trip odometer mileages closely.
Low fuel light may come on perhaps as early as 13 gallons gone-tank holds 18.1 or 18.5 depending who you ask.
Lots of threads out there so read up....