Exhaust Gas Recirculation: Description and Operation

Fig. 43 Exhaust Gas Recirculation System Controls:

The EGR system is designed to reduce the emission of oxides of nitrogen (NOx), by recirculating exhaust gas through the EGR valve and the intake manifold into the combustion chambers. The EGR system is composed of the EGR valve, constant vacuum control (CVC) valve, EGR control solenoid valve, ECU (PGM TBI control unit) and various sensors.
The ECU contains memories for ideal EGR valve lifts for varying operating conditions. The EGR valve lift sensor detects the position of the EGR valve and sends the information to the ECU. The ECU then compares it with the ideal valve lift as determined by signals from other sensors. To control the position of the EGR valve, the ECU varies the current to the EGR control solenoid valve to control the vacuum applied to the EGR valve.