System Description

DIAGNOSTIC SYSTEM DESCRIPTION
The engine control module (ECM) contains a built-in self-diagnosis system which detects troubles within the engine signal network and a malfunction indicator lamp (MIL) ("CHECK" lamp) on the instrument panel which is used to indicate the stored code.
By analyzing various signals ECM detects system malfunctions which are related to the various operating parameter sensors or actuators. The ECM stores the diagnostic code associated with the detected failure until the diagnosis system is cleared by removing the 15 Amp EFI fuse with the ignition switch OFF.

Location Of Malfunction Indicator Lamp (Check Engine Light).:

The "CHECK" light (MIL) on the instrument panel informs the driver that a malfunction has been detected.
The light goes off automatically when the diagnostic codes have been cleared.

MALFUNCTION INDICATOR LAMP (MIL) - ("CHECK" ENGINE LIGHT)
1. The malfunction indicator lamp will come ON when the ignition switch is placed at ON and the engine is NOT RUNNING.
2. When the engine is started, the MIL should go OFF.
If the light remains ON, the diagnosis system has detected a malfunction or abnormality in the system.

2 TRIP DETECTION LOGIC:
Certain data trouble codes (DTC) (21, 25, 26, 27 and 71), can be triggered by driving conditions without a malfunction present. To improve self diagnostic reliability, "2nd trip" detect logic is used.

When any a fault related to any of the above DTC's is detected, the ECM retains a temporary record of the fault in memory. An actual code is set only if the same fault is recorded during the next ignition/driving cycle.
The MIL is only illuminated after the "2nd trip."
Because the ECM must see the fault for 2 consecutive trips, the chances of a false code are greatly reduced.


DIAGNOSIS
A specific driving pattern must be followed to recreate a fault code.

Two Trip Detection Logic - Driving Pattern:

^ Drive the vehicle in the same manner the customer has indicated caused the fault.
^ Stop vehicle and turn ignition OFF.
^ Restart vehicle and repeat test-drive.

BACK-UP FUNCTION
It there is trouble with the program in the ECM and the ignition signals (IGT) are not output from microcomputer, the ECM controls fuel injection and ignition timing at predetermined levels as a back-up function to make it possible to continue to operate the vehicle.
Furthermore, the injection duration is calculated from the starting signal (STA) and the throttle position signal (IDL). Also, the ignition timing is fixed at the initial ignition timing, 5° BTDC, without relation to the engine speed.

HINT: If the engine is controlled by the back-up function, the malfunction indicator lamp lights up to warn the driver of the malfunction but the diagnostic trouble code is not output.

VERIFICATION OF REPAIR
After repairs, clear ECM memory and follow the same driving pattern used for code detection.