EGR Control Solenoid: Description and Operation

Exhaust Gas Recirculation (EGR) Bypass Valve
In order to check the EGR passage and its valve for restrictions, the Powertrain Control Module (PCM) turns the EGR bypass valve ON, allowing manifold vacuum to the EGR valve, forcing the valve to open. When this happens, the PCM checks for variations in intake manifold pressure. The PCM can check whether the EGR passage or the valve have any restriction by comparing actual Manifold Absolute Pressure (MAP) sensor readings against expected values. The PCM activates the EGR Bypass Valve only when it diagnoses the EGR system.