Exhaust Gas Recirculation (EGR) gases are regulated by the Engine Management System (EMS). The EGR opens and closes based on engine coolant temperature, engine speed, vehicle speed, throttle angle and manifold absolute pressure (MAP). The operation of the EGR system is monitored by the EMS that allows gases to flow at a calculated rate and compares it against MAP sensor and oxygen sensor activity`. The EMS anticipates an increase in MAP voltage and an increase in O2 sensor voltage.
Electrically operated vacuum control solenoids used to control the flow of vacuum to the EGR valve rely on pulse-width duty cycle commands from the EMS to control its operation. Using input values and the operating conditions previously mentioned the EMS completes the electrical circuit for the solenoid to allow vacuum operation of the EGR.
In addition to solenoids controlling vacuum flow the incorporation of a back pressure transducer regulates vacuum signals independently of electrical signals. When back pressure in the exhaust system is low the transducer pintle is open and manifold vacuum is allowed to bleed off. As back pressure increases the amount of vacuum allowed to bleed off is reduced resulting in more vacuum being applied to the valve. This allows air pressure to open the valve.
A faulty EGR system can exhibit the following symptoms due to loose connection, bad grounds, high-resistance in the circuit, or open circuits: