On Board Diagnostic (OBD) System: 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: Identifying SAE Modes Associated With Emission-Related Diagnostics

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

The above information can be checked using procedures listed in Fig 2 .

Fig 2: Identifying Information Verified Using On Board Diagnostic (OBD) Systems

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  .