An EGR switch consists of a valve, vacuum and solenoid. When a vehicle's combustion temperature rises above 1,371 degrees C, the EGR valve opens and the vacuum draws in exhaust to help balance out harmful emissions. The EGR solenoid controls the vacuum process through the valve and if it malfunctions, major problems can develop.
A solenoid consists of a coil connected to a plunger that opens or blocks the EGR vacuum. It has 4 wires that are triggered by the power control module to turn the vacuum on or off and monitor its position.
The EGR vacuum will not operate if the power control module does not signal the solenoid to switch it on. Also, faulty wiring of the solenoid can cause overstimulation of the vacuum, creating a stronger suction than needed. As a result, the EGR valve may become clogged or open too widely. Both of these actions can cause emissions and drivability problems.
Some symptoms of a faulty solenoid include poor idle, poor acceleration, stalling, low engine vacuum and hesitation or rough riding while driving.