Theory of Operation
WARNING: This page is about a different car, the 2011 RAM Pickup. However, it is still accessible from the selected car via links, so may be relevant.
The engine aftertreatment system monitors the oxygen content in the exhaust. The Powertrain Control Module (PCM) monitors the exhaust gases for oxygen content and varies the fuel injector on time to control the intake air fuel mixture. This monitor checks the O2 Sensor 1/1 at zero fueling condition, when the oxygen concentration in the exhaust should be close to air. The PCM will illuminate the MIL lamp if it detects that the actual O2 measurement does not match the expected value in two drive cycles. The PCM will turn off the MIL lamp after the monitor runs and passes in four consecutive drive cycles.