Introduction to On Board Diagnostics (II)
Introduction to On Board Diagnostics (II)
Introduction to On Board Diagnostics (II)
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Sensors and Actua<strong>to</strong>rsEmployed in OBD <strong>II</strong>EGR actua<strong>to</strong>r<strong>Diagnostics</strong>Principle of operationThe EGR actua<strong>to</strong>r is a vacuum operateddiaphragm valve, with a spring that holds the valve closed if no vacuum is applied.The vacuum that operates the diaphragm is supplied by the intake manifold and iscontrolled by a solenoid operated valve under control of the PCM. When thesolenoid is energized by the PCM the EGR valve is opened by the applied vacuum.When the solenoid is deenergized the the vacuum is cut off from the EGR valve andthe spring holds the EGR valve closed. The amount of EGR is controlled by theduty cycle of the pulsed control current that is proportional <strong>to</strong> the average time ofenergized solenoid. The duty cycle, and the valve opening are properly controlled<strong>to</strong> ensure exact amount of EGR is provided without adversely affecting emissions.The duty cycle of the current pulse that energizes the solenoid ,<strong>Diagnostics</strong> and the EGR amount are correlated periodically by OBD <strong>II</strong>diagnostics.OBD <strong>II</strong> DTCs The failure modes of EGR flow are diagnosed by OBD <strong>II</strong>. DTCs for these faultsare 400-408.
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