Introduction

The ECM (ECCS control module) has an on board diagnostic system, which detects malfunctions related a to engine sensors or actuators. The ECM also records various emission-related diagnostic information including:
- 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
The above information can be checked using procedures listed in the table below.
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.

TWO TRIP DETECTION LOGIC
When a malfunction is detected for the first time, 1st trip DTC and 1st trip Freeze Frame data are stored in the ECM memory. The MIL will not light up at this stage. <1st trip>
If the same malfunction is detected again during the next drive, the DTC and Freeze Frame data are stored in the ECM memory, and the MIL lights up. The MIL lights up at the same time when the DTC is stored. <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 light up or blink the MIL and store DTC and Freeze Frame data, even in the 1st trip, as shown.