Originally Posted by Kidd_Funkadelic
Seems as though the gauge isn't very accurate?
The DEF tank ultrasonic fill level sensor is highly inaccurate, so these stories make sense.
This is why the manufacturer stipulates you must add at *least* 1 gallon of DEF when refilling. If less than that amount is added then the algorithm will assume that the sensor is going crazy again and will ignore the new fill level.
Don't worry about the gauge accuracy as long as you have a DEF injector protection plate. You'll always have plenty of warning unless the wimpy plastic DEF injector (that a child could wiggle around with a single finger) gets sheared off by driving over a puddle on the road and then leaks out all of your DEF like a severed artery.