Exhaust Gas Recirculation: Description and Operation

View: EGR System Vacuum Hose Schematic:

SYSTEM DESCRIPTION
This system cuts and controls vacuum applied to the EGR valve to suit engine operating conditions. This cut-and-control operation is accomplished through the ECM and the EGR valve & EVAP canister purge control solenoid valve. When the ECM detects any of the following conditions, current flows through the solenoid valve. This causes the port vacuum to be discharged into the atmosphere. The EGR valve remain closed.
- Low engine coolant temperature
- Engine starting
- Engine stopped
- Engine idling
- Excessively high engine coolant temperature
- Mass air flow sensor malfunction
- Low vehicle speed

ON-BOARD DIAGNOSIS LOGIC
If the absence of EGR flow is detected by EGR temperature sensor under the condition that calls for EGR, a "Low Flow" malfunction is diagnosed.
If EGR temperature sensor detects EGR flow under the condition that does not call for EGR, a high-flow malfunction is diagnosed.