On-Board Diagnostics

Diagnostic Connectors:

PURPOSE
The self-diagnosis system detects, stores and has provision for reading codes indicating various faults with electronic engine and emission controls. A "CHECK ENGINE" light on the instrument panel indicates the presence of trouble codes and flashes the codes. The system has a fail-safe function which will default to a preset value when a part is judged defective, thereby maintaining minimal driveability until repairs can be made.

On-Board Diagnostics:

OPERATION
For accessing codes, two connectors (Read Memory and Test Mode) and the "CHECK ENGINE" are used. The connectors are for mode selection and the lamp monitors the type of problem. Read Memory connectors are black and Test Mode connectors are green. Both connectors are under the dash.

The self-diagnosis system has four modes:

^ U-Check Mode:
Only components necessary for proper starting and drive operation are monitored. The "CHECK ENGINE" light will come on when a fault is detected, indicating the need for further diagnosis. Parts which do not significantly affect starting or driveability are not monitored in this mode.

^ Read Memory Mode:
This mode is used to read codes of past problems stored in memory and can be accessed when the "CHECK ENGINE" light is off. It is effective for detecting poor contact or loose electrical connections.

^ D-Check Mode:
This mode checks the entire system and displays any trouble codes currently being monitored.

^ Clear Memory Mode:
This mode removes trouble codes from memory after repairs are made.

RELATIONSHIP BETWEEN MODES AND CONNECTORS

^ U-CHECK MODE:
Ignition "ON," Read Memory disconnected, Test Mode disconnected.

^ READ MEMORY MODE:
Ignition "ON," Read Memory connected, Test Mode disconnected.

^ D-CHECK MODE:
(engine on)
Ignition "ON," Read Memory disconnected, Test Mode connected.

^ CLEAR MEMORY MODE:
(engine on)
Ignition "ON" (engine on), Read Memory connected, Test Mode connected.