Displaying and Reading Trouble Codes

Fig. 1 ALDL Connector:

Less Scan Tool
When the diagnostic terminal (Fig. 1) is grounded with the ignition ON and the engine OFF, the system will enter its diagnostic mode and the following will be displayed.
1. The `Service Engine Soon' light will flash a code 12, indicating system is operating properly.
2. Stored codes are displayed by flashing the `Service Engine Soon' light. Each code will flash three times, then code 12 will flash again.
3. All ECM controlled relays and solenoid will be energized.

With Scan Tool
Connect TECH 1 Diagnostic Scan tool or equivalent to ALDL connector, which is located under the instrument panel and is sometimes covered by a plastic cover. Follow manufacturer's instructions for accessing codes.