Exhaust Gas Recirculation: Description and Operation

CIRCUIT DESCRIPTION
The Exhaust Gas Recirculation (EGR) system is designed to recirculate the exhaust gas properly controlled according to the driving condition back into the intake air-fuel mixture. It helps to slow down combustion in the cylinder and thus lower the combustion temperature which, in turn, reduces the amount of NOx emission. The amount of EGR is regulated by the EGR vacuum modulator according to the engine load.

If even one of the following conditions is fulfilled, the Vacuum Switching Valve (VSV) is turned ON by a signal from the Engine Control Module (ECM). This resuits in atmospheric air acting on the EGR valve, closing the EGR valve and shutting off the exhaust gas (EGR cut-OFF).
- Engine coolant temp. below 50°C (122°F)
- During deceleration (throttle valve closed)
- Light engine load (amount of intake air very small)
- Engine speed over 5,200 rpm
- Traction control is operating