Description of On-Board Diagnostics

CLOSED LOOP EMISSION CONTROL DIAGNOSIS (for California)

General
The Closed Loop Emission Control system has a self-diagnostic system which will cause the "CHECK ENGINE" lamp on the instrument panel to ramian "on" when the engine is running. This is an indication that there is a fault in the system. If this is the problem, refer to the Diagnostic Circuit Check chart Fig. E-2. Diagnostic Circuit Check

Before suspecting a problem in the Closed Loop Emission Control system that is not "CHECK ENGINE" lamp related, perform appropriate Engine Performance Diagnosis for complete diagnosis.

When diagnosing the System, open circuits are often difficult to locate by sight because oxidation or terminal misalignment are hidden by the connectors. Merely wiggling a connector on a sensor or in the wiring harness may correct the open circuit condition. This should always be considered when an open circuit or failed sensor is indicated while troubleshooting the System.

The Closed Loop Emission Control System diagnosis starts in sequence with the following charts:
1. Diagnostic Circuit Check chart
2. Driver Complaint
3. System Performance Check chart

It is important that these charts be followed in a step-by-step sequential procedure without leaving out a step or assuming the solution to the problem. If charts are not followed, the system will be improperly diagnosed.

Although there are many charts and trouble codes connected with the system diagnostics, only two charts are needed to prove the system is properly operating. Normally, only three charts are needed to diagnose and repir a problem. If the ECM connectors need to be disconnected during diagnosis, be sure that the ignition switch is in the "OFF" position before disconnecting a connector.

Fig. E-1:

Figure E-1 summarizes the system diagnosis procedure.