On-Board Diagnostic System

PURPOSE
The engine control module contains a built-in, self-diagnosis system by which troubles with the engine signal network are detected and a malfunction indicator lamp on the combination meter lights up. By analyzing various signal the engine control module detects system malfunctions relating to the sensors or actuators.

OPERATION
The On-Board Diagnostic system operates as follows:

The self-diagnosis system has 2 modes, a normal mode and a test mode.

If a malfunction is detected when in the normal mode, the engine control module lights up the malfunction indicator lamp to inform the driver of the occurrence of a malfunction. (For some codes the light does not come on.) The light goes off automatically when the malfunction has been repaired. But the diagnostic trouble code(s) remains stored in the engine control module memory. The engine control module stores the code(s) until it is cleared by removing the EFI fuse with the ignition switch to LOCK.

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 are connected. When 2 or more codes are indicated, the lowest number (code) will appear first.

If a malfunction is detected when in the test mode, the engine control module lights up the malfunction indicator lamp to inform the technician of the occurrence of a malfunction (except for code Nos. 43, 51 and 53). In this case, TE2 and E1 terminals on the data link connector 1 should be connected.

In the test mode, even if the malfunction is corrected, the malfunction code is stored in the engine control module memory even when the ignition switch is to LOCK (except code Nos. 43, 51 and 53). This also applies in the normal mode. 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 on the data link connector 1.

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 can be implemented by the technician following the appropriate procedures of check terminal connection and operation.