On Board Diagnostic System Function: Notes

The on board diagnostic system has the following four functions.

Fig 1: On Board Diagnostic System Function

Courtesy of NISSAN MOTOR CO., U.S.A.

When there is an open circuit on MIL circuit, the ECM cannot warn the driver by lighting MIL up 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.

Fig 2: Fail-Safe Function Chart

Courtesy of NISSAN MOTOR CO., U.S.A.