What does it mean when the DEF light is on in a truck?

[VanAaliyah]

Truck DEF light on indicates that the car's auxiliary water tank is short of water. If the small odometer on the dashboard displays DEF, it means there is a fault with the internal processor of the dashboard. The following is an introduction about the water tank: 1. Concept: The car water tank, also known as the radiator, is a major component of the car cooling system. Its function is to dissipate heat. The coolant absorbs heat in the water jacket, flows to the radiator to dissipate the heat, and then returns to the water jacket to circulate, achieving temperature regulation. It is part of the car engine. 2. Working principle: The water tank is an important component of a water-cooled engine. As a key part of the cooling circuit of a water-cooled engine, it can absorb heat from the cylinder block and prevent the engine from overheating. Since water has a relatively large specific heat capacity, the temperature does not rise much after absorbing the heat from the cylinder block, so the engine's heat is dissipated through the liquid circuit of the coolant.