System Operation

PURPOSE



The Engine Control Module (ECM) contains a built-in self-diagnosis system by which troubles with the engine signal network are detected and a Malfunction Indicator Lamp (MIL) in the combination meter lights up.

OPERATION
By analyzing various signals (as shown in 'Trouble Code Descriptions') the ECM detects system malfunctions relating to the sensors or actuators.

Normal Mode
In the normal mode, the self-diagnosis system monitors 13 (for California specification vehicles) or 11 (for other than California specification vehicles) items, indicated by code No. as shown in '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. The ECM stores the code(s) until it is cleared by removing the "EFI" 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 (DLC1) are connected. When 2 or more codes are indicated, the lowest (numbered) code will appear first.

Test Mode
In the test mode, 10 (for California specification vehicles) or 8 (for other than California specification vehicles) items, indicated by code No. as shown in Trouble Code Descriptions are monitored. If a malfunction is detected in any one of the systems indicated by code numbers 13, 21, 22, 24, 25, 26, 27, 31, 41 and 71 (for California specification vehicles) or 13, 21, 22, 24, 25, 26, 31 and 41 (for other than California specification vehicles) 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 (DLC1) should be connected.

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. 43 and 51). This also applies in the normal mode. The diagnostic mode (i.e.. Normal or Test) and the output of the malfunction indicator lamp can be selected by connecting the TE1, TE2 and E1 terminals on the DLC1.

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 diagnosis system. The test mode can be implemented by technician following the appropriate procedures of check terminal connection and operation described in 'How to Display and Read Diagnostic Trouble Codes'.