Def Gauge

WARNING: This page is about a different car, the 2017 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.

The Diesel Exhaust Fluid (DEF) gauge gives an indication to the vehicle operator of the level of DEF in the DEF tank. This gauge is controlled by the instrument cluster circuit board based upon cluster programming and a bus message received by the cluster. This bus message is based upon a hard-wired input received by the Body Control Module (BCM) from the DEF level sending unit, located in the DEF tank.

The DEF gauge is a stepper motor design unit that receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The Instrument Panel Cluster (IPC) electronic circuitry controls the gauge needle position.

The BCM continually monitors the DEF tank sending unit to determine the level of fuel in the fuel tank. The BCM then sends the proper electronic fuel level message to other electronic modules in the vehicle over the Controller Area Network (CAN) data bus.

NOTE:

When the DEF tank temperature is less than 14°F (-10°C), DEF may be frozen and the urea gauge in the cluster will use the last valid reading at last key-off. When the DEF tank warms up to a temperature that is greater than or equal to 14° F (-10°C), the urea gauge in the cluster will update. This is due to the increased error in level sensing at DEF tank temperatures less than 14°F (-10°C) due to DEF fluid freezing.