Introduction

The ECM (ECCS control module) has an on board diagnostic system, which detects engine system malfunctions related to sensors or actuators. The ECM also has a memory function which detects various emission-related diagnostic information. This includes:
- Diagnostic Trouble Code (DTC) .... Mode 3 of SAE J1979
- Freeze Frame data .... Mode 2 of SAE J1979
- System Readiness Test (SRT) code .... Mode 1 of SAE J1979
- 1st Trip Diagnostic Trouble Code (1st Trip DTC) .... Mode 7 of SAE J1979
- 1st Trip Freeze Frame data
- Test values and Test limits .... Mode 6 of SAE J1979
These data can be verified using procedures listed in the accompanying table.
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.