Intro, 2 Trip Detection Logic, MIL, OBD System Function, Freeze Frame Data

INTRODUCTION
The 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 shown in image.




MALFUNCTION INDICATOR LAMP
1. The malfunction indicator lamp will light up when the ignition switch is turned ON without the engine running. This is a bulb check.
2. When the engine is started, the malfunction indicator lamp should go off.
If the lamp remains on, the on-board diagnostic system has detected an engine system malfunction.




ON-BOARD DIAGNOSTIC SYSTEM FUNCTION
The on-board diagnostic system has the following four functions.
1. BULB CHECK:
This function checks the MIL bulb for damage (blown, open circuit, etc.).
2. MALFUNCTION WARNING:
This is a usual driving condition. When a malfunction is detected twice (two trip detection logic), the MIL will light up to inform the driver that a malfunction has been detected.
Only the following malfunctions will light up or blink the MIL even in the 1st trip.
- "Misfire (Possible three way catalyst damage)"
- "Three way catalyst function"
- "Closed loop control"
3. SELF-DIAGNOSTIC RESULTS:
This function allows diagnostic trouble codes to be read.
4. FRONT HEATED OXYGEN SENSOR MONITOR:
This function allows the fuel mixture condition (lean or rich), monitored by front heated oxygen sensor, to be read.

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 following priorities to update the data.




For example, an 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.