Description of On-Board Diagnostics

The PCM performs an on-board diagnostic check of the EGR system. The diagnostic system uses the electronic EGR transducer for the system tests.

The diagnostic check activates only during selected engine/driving conditions. When the conditions are met, the PCM energizes the transducer solenoid to disable the EGR. The PCM checks for a change in the heated oxygen sensor signal. If the air-fuel mixture goes lean, the PCM will attempt to enrichen the mixture. The PCM registers a Diagnostic Trouble Code (DTC) if the EGR system is not operating correctly. After registering a DTC, the PCM turns on the malfunction indicator (Check Engine) lamp after 2 consecutive trips. There are 2 types of failures sensed by the PCM. The first is a short or open in the electrical solenoid circuit. the second is a mechanical failure or loss of vacuum. The Malfunction Indicator Lamp (MIL) indicates the need for service.

If a problem is indicated by the MIL and a DTC for the EGR system is set, check for proper operation of the EGR system. Use the System Test, EGR Gas Flow Test. If the EGR system tests properly, check the system using the DRB scan tool. Refer to On-Board Diagnosis. Also, refer to the DRB scan tool and the appropriate Powertrain Diagnostics Procedure.