Theory Of Operation

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) Tank Level Sensor and Diesel Exhaust Fluid (DEF) Tank Temperature Sensor are to measure the level and temperature of the fluid inside the DEF Tank. Though integrated with the DEF Supply Pump the level sensor and the temperature sensor operate independently. The temperature sensor operates as a typical two wire 5-Volt sensor. The level sensor operates as a typical three wire 5-Volt sensor. The DEF Tank Temperature Sensor is a negative temperature coefficient sensor. The sensors are not sold separately and must be replaced with the DEF Supply Pump assembly. The DEF Dosing Control Unit monitors these inputs and reports them to the Powertrain Control Module (PCM). The PCM will illuminate the MIL lamp after this diagnostic runs and fails for two consecutive trips. The PCM will turn off the MIL lamp immediately after the diagnostic runs and passes. Engine torque will be reduced if the engine is operated for an extended period of time with this fault active.

The first warning will occur when the p-code becomes pending or active. The customer will hear a chime and get an EVIC message reading "Service DEF System See Dealer." The second warning level will occur if the customer continues to drive and the code has not cleared. The customer will hear a chime and get an EVIC message reading "Speed Limited to 5 mph in XXX MILES See Dealer". Upon driving until the countdown reaches zero, the customer will hear a chime and get an EVIC message reading "5 mph Max on Restart, Long Idle or Refuel See Dealer." Upon key-off, refuel, or 1 hour long idle, the EVIC message will read, "Speed Limited to 5 mph See Dealer." Once induced to a 5 mph derate, the inducement will not clear unless the diagnostic runs and passes, or the PCM is recalibrated.