On Board Diagnostic System Description: Introduction

The ECM has an on board diagnostic system, which detects malfunctions related to engine sensors or actuators. The ECM also records various emission-related diagnostic information including:

Fig 1: Emission-Related Diagnostic Information Chart

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

The above information can be checked using procedures listed in the figure below.

Fig 2: DTC Table

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

The malfunction indicator lamp (MIL) on the instrument panel lights up when the same malfunction is detected in two consecutive trips (Two trip detection logic), or when the ECM enters fail-safe mode. (Refer to FAIL-SAFE CHART  .)

• When there is an open circuit on MIL circuit, the ECM cannot warn the driver by lighting MIL up when there is a malfunction on engine control system.

  Therefore, when electrically controlled throttle and part of ECM related diagnosis is continuously detected as NG for 5 trips, ECM warns the driver that engine control system has a malfunction 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 3: Engine Operating System Condition Chart

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