General System Description

SYSTEM DESCRIPTION
The Engine Control Module (ECM) (ECCS control module) has an on-board diagnostic system, which detects engine system malfunctions related to sensors or actuators. 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).

Two-Trip Detection Logic
When a malfunction is detected for the first time, the malfunction (DTC and freeze frame data) is stored in the ECM memory.
<1st trip> - The malfunction indicator lamp will not light up at this stage.

If the same malfunction is detected during the next drive, this second detection causes the malfunction indicator lamp to light up.
<2nd trip> - Specific on-board diagnostic items will light up or blink the MIL even in the 1st trip as below.




The "trip" in the "Two Trip Detection Logic" means performing of the "DTC Confirmation Procedure".

FREEZE FRAME DATA
The ECM has a memory function which stores the driving condition at the moment the ECM detects a malfunction. This includes fuel system status, calculated load value, engine coolant temperature, short fuel trim, long fuel trim, engine speed, vehicle speed.
Stored data is called Freeze Frame Data.

The data is useful for tracking down conditions at the time of the malfunction. Such conditions include whether vehicle was running or stopped, engine warm up, air-fuel ratio, etc.
This data can be utilized to duplicate the malfunction and to diagnose the trouble.
The data will be erased along with the diagnostic trouble code by the above-mentioned method.




The data can be stored only for the 1st trip. It can not be renewed even at the 2nd trip. The freeze frame data can be stored for only one item. Therefore, the ECM has the priorities in the chart above to update the data.

For example, an Exhaust Gas Recirculation (EGR) malfunction (Priority: 2) was detected and the freeze frame data was stored at the 1st trip. After that, misfire (Priority: 1) is detected in another trip, and freeze frame data is updated from the EGR malfunction for the misfire.