How does an EGR system work?

I never understood this one, does it just recirclelate the exhaust gas back into the combustion chamber when cold? What are the differences between the EGR valvle, EGR vacuum solinode, and the EGR position sensor?

now that I have cleaned my EGR ports, my check engine light comes on (with code 12) after I have been driving for a few miles, and then will go off a few miles later and not come back on again unless I start the engine up cold.

Thanks, this is a great site.

The egr valve is the valve that opens and closes to feed exhust back threw the intake.
The position sensor tells the pcm what position the egr valve is at or how open it is.
The solenoid is what opens and closes or regulates vacume to egr valve.
It is controlled by the pcm.
Get a good repair manual and go threw the repair flow chart for code 12.
MT

http://www.autoshop101.com/forms/h61.pdf
That's a good one, thanks!

You're welcome