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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 (see table below) the Engine Control Module (ECM) detects system malfunctions relating to the sensors or actuators.
In the normal mode, the self-diagnosis system monitors 19 items, indicated by code No. as shown (see table below). 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 Nos. 16 and 53). The ECM stores the code(s) until it is cleared by removing the EFI No. 1 fuse with the ignition switch off.
The diagnostic trouble code can be read by the number of blinks of the malfunction indicator lamp when TE1 and E1 terminals on the data link connector 1 or 2 are connected. When 2 or more codes are indicated, the lowest number (code) will appear first.
In the test mode, 13 items, indicated by code No. as shown (see table below) 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 this case, TE2 and E1 terminals on the data link connector 2 should be connected as shown later.
In the test 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. 42 and 51). This also applies in the normal mode. The diagnostic trouble mode (normal or test) and the output of the malfunction indicator lamp can be selected by connecting the TE1, TE2 and E1 terminals on the data link connector 2, as shown later.
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. This function fills up the self-diagnosis system. The test mode ca be implemented by the technician following the appropriate procedures of check terminal connection and operation described later.

Diagnosis Inspection (Normal Mode)
  • The malfunction indicator lamp will come on when the ignition switch is turned ON and the engine is not running. HINT: If the malfunction indicator lamp does not lightup, proceed to troubleshooting of the telltale light RH (See page BE-61)
  • When the engine is started, the malfunction indicator lamp should go off. If the light remains on, the diagnosis system has detected a malfunction or abnormality in the system.

  1. Turn ignition switch on.
  2. Connect terminal between TE1 and E1 of data link connector 1 or 2.
  3. Read the diagnostic trouble code from malfunction indicator lamp. HINT: If a diagnostic trouble code is not output, check the TE1 terminal circuit.
  4. Check the details of the malfunction using the diagnostic trouble code table (see table below).
  5. After completing the check, disconnect terminals TE1 and E1 and turn off the display. HINT: In the event of 2 or more malfunction codes, indication will begin from the smaller numbered code and continue in order to the larger.
List of CODES here:


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