Two Trip Detection Logic
When a malfunction is detected for the first time, 1st trip DTC and 1st trip freeze frame data are stored in the ECM memory. The MIL will not illuminate at this stage. If the same malfunction is detected again during the next drive, the DTC and freeze frame data are stored in the ECM memory, and the MIL illuminates. The MIL illuminates at the same time when the DTC is stored (2nd trip). The "trip" in the 2 trip detection logic means a driving mode in which self-diagnosis is performed during the vehicle operation. Specific on-board diagnostic items will cause the ECM to light up or blink the MIL, and store DTC and freeze frame data, even in the 1st trip as shown. See Fig 1.
When there is an open circuit on MIL circuit, the ECM cannot warn the driver by illuminating the MIL when there is a malfunction in engine control system. Therefore, when electrical controlled throttle and part of ECM related diagnosis are continuously detected as NG for 5 trips, ECM warns the driver that engine control system malfunctions and MIL circuit is open by means of operating fail-safe function. The fail-safe function also operates when diagnosis except MIL circuit are detected and demands the driver to repair the malfunction. When engine is operating in fail-safe mode, engine speed will not exceed 2500 RPM due to the fuel cut.