EGR Valve: Description and Operation

Exhaust Gas Recirculation System (North American NA Models Only)

The exhaust gas recirculation (EGR) system helps to control the nitrous oxide (NOx) content of the exhaust emissions. It does this by directing a proportion of the exhaust gasses back to the engine intake manifold, which results in a reduction of combustion temperatures and NOx emissions.
The EGR system consists of an EGR valve, an EGR valve function sensor and a transfer pipe.

EGR Valve




The vacuum operated EGR valve used in previous systems is replaced by an electrical valve to enable mapped control of valve opening by the engine control module (ECM). The new EGR valve is a variable position pintle valve, installed on the intake manifold. In the de-energized condition the pintle extends to the closed position. In the energized condition the pintle retracts to the open position. A pintle position sensor in the EGR valve supplies a feed-back signal to the ECM, for closed loop control.

EGR Valve Function Sensor




The EGR valve function sensor is a thermistor, which is connected to the ECM. The sensor is installed on the intake manifold adjacent to the EGR valve.

Transfer Pipe







The transfer pipe is a flexible steel pipe, with a flanged connector on both ends, which connects the exhaust manifold to the intake manifold.

System Operation




The ECM determines the required position of the pintle in the EGR valve from engine speed and load (mass air flow) inputs. It then energizes the EGR valve and the pintle retracts, allowing exhaust gasses through the transfer pipe to the intake manifold. From the feed-back signal of the pintle position sensor, the ECM continuously checks for any discrepancy between required and actual pintle positions and if necessary, adjusts the energizing signal to correct any error. The temperature of the recirculating gasses is supplied to the ECM by the EGR valve function sensor, for diagnostic checks of system operation.
To prevent the build-up of carbon deposits and confirm the range of movement of the EGR valve, the ECM cycles the valve from closed to fully open and back each time the engine ignition switch is set to OFF.
Operation of the system is disabled when the vehicle is stationary, the engine is at idle rpm or the engine is running at full load.
The ECM does not open the EGR valve the full amount required until the engine temperature reaches the normal operating range. As the engine temperature increases, so the ECM progressively increases the percentage of valve opening until, at an engine coolant temperature of 7O°C (158°F), the valve is at 100% of the required position.