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 Diesel Oxidation Catalyst is designed to react with hydrocarbons in the exhaust stream, this reaction produces heat. The heat can become excessive if too much hydrocarbon enters the Aftertreatment Diesel Oxidation Catalyst too quickly. Excessive heat can damage the diesel aftertreatment components, so the temperature of the aftertreatment system is closely monitored by the Powertrain Control Module (PCM). The Exhaust Temperature Sensors are used by the PCM to monitor the temperatures throughout the aftertreatment system. The Exhaust Temperature Sensors are thermistors and change resistance based on the temperature being measured. The PCM provides a calibrated reference voltage to the sensor. The PCM monitors the voltage on the signal pin 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 illuminate the MIL lamp immediately when the diagnostic runs and fails. The PCM will also disable active regeneration of the aftertreatment diesel particulate filter. This DTC will not self clear and must be cleared by a scan tool.