Electronic Control Systems: Self-diagnosis

WARNING: This page is about a different car, the 2010 Acura TL and 2009 Acura TL. However, it is still accessible from the selected car via links, so may be relevant.

The ECM/PCM detects the failure of a signal from a sensor or from another control unit and stores a Pending DTC or a Confirmed DTC. Depending on the failure, a Confirmed DTC is stored in either the first or the second drive cycle. When a Confirmed DTC is stored, the ECM/PCM turns on the malfunction indicator lamp (MIL) by a signal sent to the gauge via F-CAN.

One Drive Cycle Detection Method
When an abnormality occurs in the signal from a sensor or from another control unit, the ECM/PCM stores a Confirmed DTC and turns on the MIL immediately.
Two Drive Cycle Detection Method
When an abnormality occurs in the signal from a sensor or from another control unit in the first drive cycle, the ECM/PCM stores a Pending DTC. The MIL does not come on at this time. If the failure continues in the second drive cycle, the ECM/PCM stores a Confirmed DTC and turns on the MIL.