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Description of On-Board Diagnostics


DIAGNOSIS SYSTEM DESCRIPTION

The Electronic Control Unit (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 instrument panel flashes.

By analyzing various signals as shown in the later table the ECU detects system malfunctions which are related to the various operating parameter sensors or to the actuator.

NORMAL MODE

In the normal mode, the self-diagnosis system monitors 18 (California
specification vehicles) or 16 (Other than California specification vehicles) items, indicated by code Nos. 11, 12, 13, 14, 16, 21, 22, 24, 25, 26, 27, 31, 32, 41, 42, 52, 53 and 71 (California specification vehicles) or 11, 12, 13, 14, 16, 21, 22, 24, 25, 26, 31, 32, 41, 42, 52, and 53 (Other than California specification vehicles).

A "CHECK" engine warning light on the instrument panel informs the driver that a malfunction has been detected. The light goes off automatically when the malfunction has been cleared. Once the malfunction is cleared, the "CHECK" engine warning light on the instrument panel will go off but the diagnostic code(s) remains stored in the ECU memory (except for code Nos. 16, 43, 51 and 53). The ECU stores the failure until the diagnosis system is cleared 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 on the check connector are connected. When 2 or more codes are indicated, the lowest number (code) will appear first. However, no other code will appear along with code No.11.

TEST MODE

In the test mode, 14 (California specification vehicles) or 12 (Other than
California specification vehicles) items, indicated by code Nos. 13, 21, 22, 24, 25, 26, 27, 31, 32, 41,42, 43, 51 and 71 (California specification vehicles) or 13, 21, 22, 24, 25, 26, 31, 32, 41, 42, 43 and 51 (Other than California specification vehicles) are monitored. If a malfunction is
detected in any one of the systems indicated by code Nos. 13, 21, 22, 24, 25, 26, 27, 31, 32, 41, 43, and 71 (California specification vehicles) or 13, 21, 22, 24, 25, 26, 31, 32, 41 and 43 (Other than California specification vehicles) the ECU lights the "CHECK" engine warning light to warn the technician that malfunction has been detected. In this case, TE2 and E1 terminals on the TOYOTA DIAGNOSTIC COMMUNICATION LINK (TDCL) should be connected as shown later.

In the test mode, even if the malfunction is corrected, the malfunction is stored in the ECU memory while the ignition switch remains on (except code Nos. 43, 51 and 53). Also, when a malfunction occurs for the 12 (California specification vehicles) or 10 (Other than California specification vehicles) conditions from code Nos. 13, 21, 22, 24, 25, 26, 27, 31, 32, 41, 43, and 71 (California specification vehicles) or 13, 21, 22, 24, 25, 26, 31, 32, 41 and 43 (Other than California specification vehicles) the "CHECK" engine warning light remains on. However, once the ignition switch is turned to OFF, the ECU erases all of the malfunctions in the memory.

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 on the check connector or TDCL, as shown later.

In the ECU, 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 described later.


"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.

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