Computers and Control Systems: Testing and Inspection

Fig. 5 Self diagnosis system check:

The computer self diagnostic circuit detects and stores system malfunctions related to the various sensor and actuator circuits. By analyzing codes stored in the computer, system malfunctions can be easily diagnosed and repaired. To obtain codes stored in computer memory, proceed as follows:
1. Turn ignition switch to ON position and observe ``Check Engine'' lamp, then start engine while observing lamp.
2. If lamp fails to light with ignition switch on (engine stopped), or if lamp fails to go out or flash after engine starts, check diagnostic circuit, Fig. 5.
3. Run engine until it reaches normal operating temperature, then turn ignition switch to OFF position.
4. Ensure battery voltage is at least 11 volts, all electrical accessories are off, throttle is completely closed and transmission selector is in park or neutral.
5. Turn ignition switch to ON position, but do not start engine.

Fig. 10 Check engine connector.:

6. Connect jumper wire between terminals of check engine connector, Fig. 10

Fig. 11 Diagnostic code identification:

DIAGNOSTIC CODE INTERPRETATION

When accessed, diagnostic codes will be displayed by the ``Check Engine'' light as follows:
1. If system is normal (no codes stored in memory), lamp will flash once every 3 seconds.
2. If malfunction codes are stored in memory, lamp will flash a number of times equal to the diagnostic code number, every 3 seconds. Diagnostic codes can be identified by referring to Fig. 11.
3. If more than one code is stored, the lowest number code will be flashed first, followed by a 3 second pause before the next highest number code will flash.
4. The diagnostic code series will be flashed as long as the check engine connector is shorted with the ignition switch turned to the ON position. It should be noted that code 7 will not be stored in memory and will only flash if the TPS circuit is malfunctioning.
5. Identify malfunctions indicated by self diagnosis system using chart, Fig. 11.
6. Refer to ``CONNECTOR ID & VOLTAGE/RESISTANCE SPECS'' and ``COMPONENT TESTING'' and repair system as needed.