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 aftertreatment temperature sensors are used by the Powertrain Control Module (PCM) to monitor the engine exhaust temperatures in the aftertreatment system. The aftertreatment temperature sensors are thermistors and change resistance based on the temperature being measured. The PCM provides a 5-Volt reference voltage to the sensor. The PCM monitors the change in signal voltage and converts this to a temperature value. When the exhaust gas temperature is cold, the sensor or thermistor resistance is high. The PCM signal voltage only pulls down a small amount through the sensor to ground. Therefore, the PCM senses a high signal voltage or low temperature. When the exhaust gas temperature is hot, the sensor resistance is low. The signal voltage pulls down a large amount. Therefore, the PCM senses a low signal voltage, or a high temperature. The PCM will set the fault if it detects that the diesel oxidation catalyst inlet exhaust gas temperature sensor signal voltage is greater than a calibrated voltage (VDC) for more than a calibrated time. The PCM illuminates the MIL lamp immediately when the diagnostic runs and fails. A default value for the aftertreatment diesel oxidation catalyst inlet temperature reading will be used and active regeneration of the diesel particulate filter will be disabled. The PCM will turn off the MIL lamp immediately after the diagnostic runs and passes.