Theory Of Operation
WARNING: This page is about a different car, the 2014 RAM 1500. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) monitors the exhaust gases for oxygen content and varies the rich/lean fuel mixture of the intake air fuel mixture to adjust the system. The monitor evaluates response time of the O2 Sensor during transition from load to overrun mode using the O2 concentration (corrected for exhaust pressure) signal. The PCM will illuminate the MIL lamp when the diagnostic runs and fails.