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 Particulate Matter (PM) Sensor is used to determine the efficiency of the Diesel Particulate Filter (DPF) by measuring the amount of particulate matter (soot) remaining in the exhaust gas after the DPF. The PM Sensor is located at the outlet of the Selective Catalytic Reduction (SCR) Catalyst, and consists of a probe and module which cannot be replaced separately of each other and must be replaced as a unit. The module communicates and shares information with the Powertrain Control Module (PCM) over the J1939 Data Link. The probe contains three internal parts: a heater, a temperature sensor, and a set of particulate measuring electrodes with a high electrical resistance. During normal operation, the module will activate the heater and perform a regeneration of the electrodes to burn off any deposited soot before taking a measurement. After sensor regeneration is complete, soot particles from the exhaust gas are then collected onto the electrodes and form conductive paths between the electrodes leading to a drop of the electrical resistance. The decreased resistance results in an increased current across the electrodes, which is compared against calibrated thresholds to determine sensor functionality and DPF efficiency.

The PM Sensor internally monitors the voltage supplied to the module and compares this voltage to the battery voltage reported by the PCM.