On Board Diagnostic System

Diagnostic Socket Description:

GENERAL DESCRIPTION
The fuel injection and ignition ECU's have on-board diagnostic capabilities which are accessed through the diagnostic socket. The diagnostic socket has three diagnostic control functions as explained below.

CONTROL FUNCTION #1 (fault codes):
The on-board diagnostic system carries out continuous system checks and monitors several components during engine operation. If the ECU detects a problem in a system or component, it stores a fault code in its memory.

The fuel injection ECU can identify 16 fault codes and store 3 codes (California market vehicles can store 16 codes) in memory.

The ignition ECU can identify 8 fault codes and store 3 codes (California market vehicles can store all 8 codes) in memory.

When the engine is stopped, fault codes can be extracted from the ECU via the diagnostic socket.

CONTROL FUNCTION #2 (input device test):
Control function #2 aids the technician in checking the operation of selected ECU input devices. An acknowledgement code tells the technician if the input device is operating correctly or not.

CONTROL FUNCTION #3 (output device test):
Control function #3 aids the technician in checking the operation of selected ECU output devices. By placing your hand on the component or listening for component operation sounds, you can verify if the output device is operating.

Code Example:

DIAGNOSTIC SOCKET OPERATION:
The diagnostic socket has a button, a light diode and a selector cable. When carrying out fault tracing, the selector cable must be placed in its appropriate socket.

^ For fuel injection trouble shooting use socket 2 (of the 6 available).
^ For ignition trouble shooting use socket 6 (of the 6 available).

Codes stored in the memory are displayed by a series of flashes from the light diode in the diagnostic socket. All codes have three numbers, each ranging from 1-9. The code is read by the number of flashes delivered by the diode.

Since all codes have three numbers, each code requires three series of uninterrupted flashes. There is a three second interval between the series of flashes to make the codes easy to read.