There's no single answer to how much fuel remains in a 2003 Hyundai Santa Fe when the low fuel light illuminates. The trigger point for the low fuel light varies slightly by vehicle and even potentially by individual car due to manufacturing tolerances and sensor drift.
Generally, expect to have between 1 and 2 gallons left when the light comes on. It's best not to wait until the light illuminates before refueling; running the tank too low can damage the fuel pump.
