Theory of Operation
WARNING: This page is about a different car, the 2011 RAM Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
The Diesel Exhaust Fluid (DEF) Ambient Air Temperature Sensor is mounted to the DEF Supply Pump Assembly bracket. The Powertrain Control Module provides a 5-Volt Signal and a sensor ground circuit for the DEF Ambient Air Temperature Sensor. The DEF Ambient Air Temperature Sensor signal is provided to the DEF Dosing Control Unit via the PCM. The DEF Dosing Control Unit uses this information along with the diesel exhaust fluid temperature information to determine when the DEF System heaters need to be turned on. The PCM will turn on the MIL Lamp immediately after the monitor runs and fails and the PCM will substitute a default value for the DEF Ambient Air Temperature Sensor.