EGR System Control

EGR SYSTEM CONTROL





Overview
EGR stands for Exhaust Gas Recirculation. The purpose of exhaust gas recirculation is to reduce the content of nitrogen oxides (NOx) in the gases. Nitrogen oxides are formed at the high temperatures which prevail in the engine combustion chambers at high load.

The combustion temperature is lowered by returning a proportion of the gases to the engine, thereby reducing the nitrogen oxide level.

The EGR system is not activated when the engine is cold or idling, or when turbo boost pressure is present, all conditions at which the nitrogen oxide level is relatively low.

The EGR system consists of the following components:

^ EGR Valve (1)
^ EGR Vacuum Controller (2)
^ EGR Temperature Sensor (3)





EGR Valve
The EGR valve controls the flow of gases from the exhaust manifold to the intake manifold. The valve is controlled by the vacuum in a hose connected to the EGR vacuum controller

The valve is mounted under the intake manifold.

EGR Controller:

EGR Vacuum Controller
The EGR valve is operated by the ECM by means of the EGR vacuum controller, one terminal of which is supplied at 12 Volts from the main relay, while the second terminal is connected to the module. The ECM operates the controller by grounding the lead. The signal from the ECM is a function of the engine speed, load and temperature, among other parameters.

Combined with the ambient pressure and intake manifold vacuum, the ECM signal is converted into a control pressure by the EGR vacuum controller. This is used to operate the EGR valve through the vacuum hose.

The control signal to the EGR valve is supplied through the connection in the upper section of the controller, while the intake manifold vacuum is supplied to the lower section. The controller stabilizes the intake manifold vacuum and converts the electrical signal from the ECM into a modulated vacuum signal, which is used to operate the EGR valve.

The EGR vacuum controller is mounted on the underside of the relay shelf, above the engine cooling fan.





EGR Temperature Sensor
The EGR temperature sensor measures the temperature of the recirculated exhaust gases. The ECM monitors the operation of the EGR system by detecting variations in temperature.

The sensor is of the NTC (Negative Temperature Coefficient) type, in which the sensor resistance falls with rising temperature.

The EGR temperature sensor is mounted in the EGR valve.