System Description

SYSTEM DESCRIPTION:



The ECM contains a built-in self-diagnosis system by which system malfunctions relating to the sensors, actuators or the engine signal network are detected and a malfunction indicator lamp (MIL) on the instrument panel lights up.

"Normal" Mode Operation



In the normal mode, the self-diagnosis system monitors 19 items, indicated by code No. as listed under "Trouble Code Descriptions". A malfunction indicator lamp informs the driver that a malfunction has been detected. The lamp goes off automatically when the malfunction has been repaired. But the diagnostic trouble code(s) remains stored in the ECM memory (except for code No. 16 and 53).

Example: Diagnostic Trouble Code No.12 And No.31 Are Output Using This Blinking Pattern:

The diagnostic trouble code can be read by the number of blinks of the malfunction indicator lamp when terminals TE1 and E1 of a data link connector (DLC1 or DLC2) are connected. When 2 or more codes are indicated, the code with the lowest number will appear first, followed by codes of ascending numbers. When all stored codes have been displayed it will be repeated, in the same order, until the codes have been cleared by removing the 15 amp "EFI No.1" fuse with the ignition switch OFF.

"Test" Mode Operation



A test mode function has been added to the functions of the self-diagnosis system of the normal mode for the purpose of detecting malfunctions such as poor contact, which are difficult to detect in the normal mode. The test mode can be implemented by the technician by connecting terminal TE2 and E1 of DLC2, as described under "How To Display And Read Diagnostic Trouble Codes".
In the test mode, 13 items indicated by code numbers (DTC's) as described under "Trouble Code Descriptions", are monitored. If a malfunction is detected in any one of the systems indicated by code Nos. 13, 21, 22, 24, 25, 26, 27, 35, 41, 47, 71 and 78 the ECM lights the malfunction indicator lamp to warn the technician that malfunction has been detected.
In the test mode, as in normal mode, even if the malfunction is corrected, the malfunction code is stored in the ECM memory even when the ignition switch is OFF (except code Nos. 43 and 51). The diagnostic mode (normal or test) and the output of the malfunction indicator lamp can be selected by connecting the TE1, TE2 and E1 terminals of DLC2, as shown under "How To Display And Read Diagnostic Trouble Codes".

Fail-Safe or "Back-Up" Mode Operation
If any of the trouble codes listed in the following chart is detected, the ECM enters fail-safe mode.

Fail-Safe Chart:

If 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, 1O° BTDC, without relation to the engine speed.

NOTE: 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.