System Description

SYSTEM DESCRIPTION:



The ECM contains a built-in self-diagnosis system by which troubles with the engine signal network are detected and a malfunction indicator lamp on the instrument panel lights up.
By analyzing various signals as shown in a later table, the engine control module (ECM) detects system malfunctions relating to the sensors or actuators.

"Normal" Mode Operation
In the normal mode, the self-diagnosis system monitors 18 (for California specification vehicles) or 17 (for Federal or Canadian specification vehicles) 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).
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 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 terminals TE2 and E1 of the data link connector (DLC2), as described under "How To Display And Read Diagnostic Trouble Codes".
In the test mode, 12 items (for California specification vehicles) or 10 items (for Federal and Canadian specification vehicles), indicated by code numbers 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, 28, 35, 41, 71 and 78 (and Nos.26 and 27 for California specification vehicles ONLY) the ECM lights the malfunction indicator lamp to warn the technician that malfunction has been detected. In this case, TE2 and E1 terminals of DLC2 should be connected.
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".
Reading 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.



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.