L84sky

The Exhaust Gas Recirculation (EGR) valve is part of the emission control system. The purpose of the EGR valve is to
reduce the production of nitrogen oxides (NOx). All internal combustion engines produce NOx but formation increases
dramatically at higher combustion temperatures (above 1600 °C or 2912 °F). The EGR system reduces the combustion
temperature by diverting a small portion of the exhaust gases back into the intake manifold.




Exhaust gases are no longer combustible. There is virtually no fuel or oxygen present. Diluting the intake air with
exhaust gases makes the air/fuel charge less combustible without changing the air/fuel ratio -- an important factor
in maintaining catalytic converter efficiency.




The engine computer (PCM) opens or closes the EGR valve to control the flow of exhaust gases back to the intake manifold.




On the V6 Tracker engine the EGR valve and EGR tube are bolted to the bottom of the intake collector.




The EGR valve connects the exhaust manifold to the intake manifold.The EGR valve is normally closed. There is no
EGR flow when the engine is cold, at idle, or during hard acceleration. The EGR flow is at its peak during steady
cruising under moderate load.




The PCM controls the amount of exhaust gas recirculated to the intake by sending an elaborate set of signals to a
six-wire stepper motor inside the EGR valve.


The output from the PCM is issued in half-steps. Each half-step rotates the stepper motor 15°. After eight unique steps the pattern repeats.
It takes twenty-four half-steps to rotate the stepper motor one full turn. Full extension of the plunger shaft takes about five turns of the stepper motor.



This .gif animates the half-step process.



These are the six EGR valve pins that connect back to the PCM.




The resistance of the stepper motor coils can be measured with an ohmmeter. The PCM also evaluates EGR operation
by monitoring changes in the Manifold Absolute Pressure (MAP) sensor. When the EGR valve is commanded open and
closed the PCM anticipates a corresponding change in intake manifold pressure. If the change in MAP sensor voltage
does not correlate with the commanded input to the EGR valve, the PCM sets code P0400 and illuminates the "check engine" light.




The EGR valve can also be manually commanded to open and close from the Tech2 scanner.