Description of On-Board Diagnostics

DIAGNOSIS SYSTEM DESCRIPTION

The ECU contains a built-in, self-diagnosis system by which troubles with the engine signal network are detected and a "CHECK" engine warning light on the combination meter lights up.
By analyzing various signals, the ECU detects system malfunctions relating to the sensors or actuators.

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

If a malfunction is detected when in the normal mode, the ECU lights up the "CHECK" engine warning light 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 code(s) remains stored in the ECU memory. The ECU stores the code(s) until it is cleaned by removing the EFI fuse with the ignition switch off.

The diagnostic code can be read by the number of blinks of the "CHECK" engine warning light when TE1 and E1 terminals of the check connector 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 ECU lights up the "CHECK" engine warning light to inform the technician of the occurrence of a malfunction (except for code Nos.42, 43 and 51). In this case, TE2 and E1 terminals of the check connector should be connected as shown later.

In the test mode, even if the malfunction is corrected, the malfunction code is stored in the ECU memory even when the ignition switch is off (except code Nos.42, 43 and 51). This also applies in the normal mode. The diagnostic mode (normal or test) and the output of the "CHECK" engine warning light can be selected by connecting the TE1, TE2 and E1 terminals of the check connector.

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.





"CHECK" ENGINE WARNING LIGHT CHECK

1. The "CHECK" engine warning light will come on when the ignition switch is placed at ON and the engine is not running.

2. When the engine is started, the "CHECK" engine warning light should go off.
If the light remains on, the diagnosis system has detected a malfunction or abnormality in the system.