OBD System: Two Trip Detection Logic
OBD System: Two Trip Detection LogicWhen a malfunction is detected for the first time, 1st trip DTC and 1st trip Freeze Frame data are saved in the ECM memory. The MIL will not illuminate at this stage. [1st trip]
If the same malfunction is detected again during the next drive, the DTC and Freeze Frame data are saved in the ECM memory, and the MIL illuminates. The MIL illuminates at the same time when the DTC is saved. [2nd trip] The "trip" in the "Two Trip Detection Logic" means a driving mode in which self-diagnosis is performed during vehicle operation. Specific on board diagnostic items will cause the ECM to illuminate or blink the MIL, and save DTC and Freeze Frame data, even in the 1st trip, as shown below.
When there is an open circuit on MIL circuit, the ECM cannot warn the driver by illuminated MIL when there is malfunction on engine control system.
Therefore, when electrical controlled throttle and part of ECM related diagnoses 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 above diagnoses except MIL circuit are detected and demands the driver to repair the malfunction.
Engine operating condition Engine speed will not
in fail-safe mode rise more than 2,500 rpm due to the fuel cut
