EGR Control Solenoid: Description and Operation

EGR Frequency Valve:

PURPOSE
The frequency valve controls the amount of vacuum supplied to the EGR valve by switching between the connection to the EGR valve and the intake air bellows.

LOCATION
Mounted on the back of the intake manifold.

OPERATION
The amount of recirculated exhaust gas is determined by the ECM, depending on engine speed and load conditions. The ECM controls the ground circuit. Voltage (12 VDC) is supplied by the Motronic power supply relay.

Control pressure (vacuum) is formed in the frequency valve from intake manifold pressure and atmospheric pressure. This control pressure is applied to the EGR valve via the EGR frequency valve. A membrane valve limits applied vacuum to 200 mbar.

Electrical Malfunction
The ECM monitors the valve for both short and open circuits. If the EGR frequency valve fails electrically, no vacuum is applied to the EGR valve.

Mechanical Malfunction
If the EGR frequency valve fails mechanically (no vacuum or continuous vacuum) a fault is registered by the EGR temperature sensor.