Section IV Steps for Trouble Diagnosis Based on Engine Symptom Before the steps for trouble diagnosis based on engine symptom, carry out the following primary checks at first: 1. Check the ECU and MIL for abnormal condition (for vehicles without MIL, skip this step); 2. To confirm no trouble information record found with a trouble diagnostic instrument or flasher; 3. Check the idle speed data after warm-up of the electronic control system with a trouble diagnostic instrument for normal range; 4. Confirm the concern of the user and the actual location of the symptom. Then, check the appreance: 1. Check the harness grounding for cleanness and tightness; 2.
Check the vacuum pipe for break, twist and correct connection; 3. Check if the pipe is blocked; check if the inlet pipe is extruded or damaged; 4. Check the sealing between the throttle body and the intake manifold for damage; 5. Check the high voltage wire of the ignition system for break, aging and wrong connection; 6. Check the lead for correct connection and check the connector for looseness. Key note: In case of the above-mentioned conditions, repair these troubles at first. Otherwise, the following trouble diagnosis and maintenance will be affected. Diagnosis help: 1. To confirm no trouble record found for the engine; 2. To confirm the concern of the user; 3.
No abnormal condition is found after check following the above-mentioned steps; 4. During check and maintenance, do not ignore the impact on the system from the vehicle maintenance, cylinder pressure, mechanical ignition timing, fuel condition, and so on. 5. Replace the ECU, and then carry out tests. If the trouble is removed at this moment, the trouble is produced within the ECU. If the trouble can not be removed at this moment, replace the original ECU, and repeat the steps. 66