Computers and Control Systems: Description and Operation

Fuse/Relay Panel Showing Fuel Pump Relay w/Fuse Receptacle:

Both the ignition control unit and fuel injection control unit have a fault memory for self diagnosis. These fault memories constantly monitor the systems' sensors, wiring and input signals.
If a problem or fault develops, these memories will store this information and take corrective action.

EXAMPLE: The engine coolant temperature sensor develops an open circuit. Both control units will now assume a calculating value of a fully warmed engine.

The fault information stored in the memories can be displayed by a flashing code of the engine control indicator light. This display is activated by inserting a spare fuse in the top of the fuel pump relay.
The indicator light will also come on while driving if:
- The ignition timing is being fully retarded because of ignition knock.
- A problem develops with the knock sensor.













The fault display is activated by inserting a spare fuse into the top of the fuel pump relay for 4 seconds. This connects the diagnostic terminals to ground. When the fuse is removed, the indicator light will then flash in a certain sequence.
Any faults stored in the control unit's memory will be displayed in steps. To move to the next step, the fuse must be reinserted for another 4 seconds.
When making the input checks, the car must be driven 5 minutes to insure that all necessary information is stored in the memories. If the car has a no start condition, operate the starter for 6 seconds to store the necessary inputs.
Do not switch the ignition off after driving the car or operating the starter. This will erase the fault memory.
This self diagnosis procedure can also be used to check the systems' outputs. If the fuse is inserted with the ignition switched off, the system switches to the output checks when the ignition is turned on. See page #32. zzzzz
The four digit codes are displayed by the flashing of the indicator light. The code will continue to repeat until the display is switched to the next step.