Diagnostic System
The ECM of the Closed Loop Emission Control system is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, the ECM will light the amber "CHECK ENGINE" light located on the instrument panel. When a malfunction is detected and light is turned on, and a corresponding trouble code is stored in ECM memory.
As a bulb and system check, the "CHECK ENGINE" light will glow when ignition switch is on and engine is not running. When engine is started, the light should go out after 1-4 seconds. If not, a malfunction has been detected in the Closed Loop Emission system.
NOTE:
Trouble codes will be recorded at various operating times. Some codes require operation of sensor or switch for 5 seconds; others require operation for 5 minutes or more.
Diagnosis of the Closed Loop Emission system is done in the following order:
- Ensure all engine systems NOT related to the system are fully operational. DO NOT proceed with testing unless all other problems have been corrected.
- Ensure that all electrical and vacuum connections are correct and in good condition.
- Enter diagnostic mode and record trouble codes flashed by "CHECK ENGINE" light. Exit diagnostic mode.
- Distinguish between fixed or intermittent trouble codes.
- If trouble codes were displayed, go to Diagnostic Circuit Check chart. Follow instructions given in chart.
- If no trouble codes were recorded, go to Driver Complaint chart and follow instructions given there.
- After any repairs are made, perform System Performance Check. Clear any trouble codes.