Reading Diagnostic Trouble Codes

Fig. 31 Check Connector Test Harness:

Before considering the ECU system as cause for complaint, ensure the battery is fully charged and the engine and all related systems are operating properly. When diagnosing ECU malfunctions, observe all precautions and follow procedures as outlined to ensure successful repairs.
The ECU self diagnosis circuit detects and stores system malfunctions related to the various sensor and actuator circuits. These malfunctions are stored as codes in the ECU as long as battery voltage is applied to the ECU and the Check Engine lamp will remain on as long as the malfunction is present. By analyzing these codes, system malfunctions can be easily diagnosed and repaired.
To obtain codes stored in the ECU memory, close throttle valve fully and turn off all accessories, then proceed as follows:

1. Short terminals of check connector with check connector test harness No. 09991-87702-000, Fig. 31.
2. Turn ignition switch On. Do not start engine.
3. Diagnosis codes stored in the ECU will cause the Check Engine warning lamp to flash.