EGR Valve: Description and Operation

The EGR valve is a stepper motor design. A stepper motor (6) drives a worm gear, that is in mesh with a spring (1) loaded plunger (5). The valve (2) end of the plunger (4) controls the flow of exhaust gases (3). The plunger movement is controlled by the powertrain control module (PCM). By turning the stepper motor in different directions, the PCM controls the opening of the exhaust gas passage to the intake manifold.

Operation
The PCM uses the inputs from various sensors in order to control the operation of the EGR valve. Information from the ECT sensor, the TP sensor, the VSS sensor, and the MAP sensor are critical for proper EGR valve operation. Under heavy engine loads, when the demand for power is high, the EGR valve is closed. In order to insure a smooth idle and stable engine operation, the EGR valve is also closed at closed throttle engine operation. The EGR valve is usually open during low and medium engine loads and speeds. Combining preprogrammed engine calibrations with various sensor inputs, the PCM calculates the optimum opening of the EGR valve.

Results Of Incorrect Operation of the EGR System
Excessive EGR valve flow may cause any of the following conditions:
- The engine stalling
- Rough idle, surging, or engine hesitation
- Lower fuel economy
- Incomplete combustion and high exhaust emissions

Inadequate EGR valve flow may cause any of the following conditions:
- Engine detonation
- Excessive exhaust emissions