The EGR (exhaust gas recirculation) position sensor is a variable resistor sensor that is monitored by a vehicle's on-board computer to verify that the EGR valve is functioning properly. A reference voltage is supplied to the sensor by the computer, and the resistance of the sensor changes as the EGR valve is opened and closed. As the vacuum operated diaphragm in the valve opens the valve, the sensor's spring-loaded pintle is moved up in the sensor. This changes the resistance in the sensor.
Attach the positive (red) meter lead to the sensor's "Signal Return" wire (the middle wire on most EGR position sensors) by pushing it into the back of the EGR position sensor's wiring connector until you feel it contact the terminal inside. Attach the negative (black) meter lead to the engine block.
Start the engine. The voltage displayed on the meter should be between .24 and .67 volts with the engine at idle. Turn off the engine but leave the ignition key in the "Run" position.
Unplug the vacuum line from the vacuum port side of the EGR valve. Apply four inches of vacuum to the EGR valve's vacuum port using a handheld vacuum pump. The voltage displayed on the meter should change to a range of 2.15 to 2.65 volts
Apply eight inches of vacuum to the EGR valve and observe the meter. The displayed voltage should now be 3.9 to 4.4 volts. Replace the EGR valve position sensor if it is out of range during these tests, or if the voltage suddenly drops to 0 volts as vacuum is applied.
