Diagnostic Procedure
NOTE:
Trouble codes will be recorded at various operating times. Some codes require operation of sensor or switch for 5 seconds; other components require operation for 5 minutes or longer at normal operating temperature, vehicle speed, and load. Therefore, some codes may not set in service bay and may require road testing vehicle to duplicate the condition under which the code will set.
Diagnosis of computerized engine control system should be performed in the following order:
- Ensure all engine systems other than computerized systems i.e., compression, ignition, etc.) are operating properly. DO NOT proceed with testing unless all other problems have been repaired. If MIL light is on, see RETRIEVING CODES WITH MIL LIGHT. For diagnosing hard codes, see TROUBLE CODE DEFINITION under DIAGNOSTIC TESTS to determine cause of malfunction.
- For diagnosing intermittent codes, proceed to INTERMITTENTS in TESTS W/O CODES - 1.5L article. Inspect condition of system harness by conducting recommended voltage or continuity checks. See appropriate WIRING DIAGRAM in WIRING DIAGRAMS section for additional information on specific circuit configuration. Inspect condition of individual component. Repair or replace component as needed.
- Recheck system operation after repair is made. If trouble code still exists, substitute known good ECM. After repairs have been completed, clear trouble codes. See CLEARING CODES .