On-Board Diagnostic System

PURPOSE
The Engine Control Module (ECM) contains a built-in self diagnostic system by which malfunctions within the engine signal network are detected. By analyzing various signals, the ECM can detect a malfunction and a Diagnostic Trouble Code (DTC) is stored in its memory for help with diagnosis. At the same time the Malfunction Indicator Lamp (MIL) on the combination meter lights up to indicate the ECM has detected a malfunction and stored the DTC.

OPERATION
The On-Board Diagnostic system operates as follows:

In the normal mode, the self-diagnosis system monitors 21 items, indicated by a code Number. 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 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, 15 items, indicated by code Number are monitored. If a malfunction is detected in any one of the systems indicated by code Nos. 13, 21, 22, 24, 25, 26, 27, 28, 29, 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 1 or 2 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 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 1 or 2.

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.