Description of On-Board Diagnostics

DIAGNOSIS SYSTEM DESCRIPTION



The ECM contains a built-in self-diagnosis system by which troubles with the engine signal network are detected and a Malfunction Indicator Lamp on the instrument panel lights up. By analyzing various signals as shown in the later table the Electronic Control Module (ECM) detects system malfunctions relating to the sensors or actuators.
In the normal mode, the self-diagnosis system monitors 14 (California specification vehicles) or 13 (Federal specification vehicles) items, indicated by code No. as shown. 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 ofthe 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 number (code) will appear first.
In the test mode, 10 (California specification vehicles) or 9 (Federal specification vehicles) 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, 31, 41 and 71 (California specification vehicles) or 13, 21, 22, 24, 25, 26, 31, 41 and 71 (Federal specification vehicles) the ECM lights the Malfunction Indicator Lamp to warn the technician that a malfunction has been detected. In this case, TE2 and E1 terminals on the 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 (normal or test) and the output of the Malfunction Indicator Lamp can be selected by connecting the TE1, TE2 and E1 terminals of DLC1.
A test mode function has been added to the functions of the self-diagnosis system for the purpose of detecting malfunctions such as poor contact, which are difficult to detect in the normal mode. The test mode can be implemented by the technician following the appropriate procedures of check terminal connection and operation described under "How to Display and Read Diagnostic Trouble Codes".