What else could cause a P0171 code on a 2006 Equinox?

Tom may be right but if that doesn't fix it try cleaning the throttle plate between the air box and the intake. They tend to get a sticky film build up on them and not close all the way. I've done that to a few over the years. It's worked every time.

Check the tube that goes from the air filter box to the firewall side valve cover. My wife was taking her 07 for oil changes and just about every time they would pop that tube out of the valve cover or break it. Once you put it back in if its out you should be able to clear the code

Was curious if you were able to clear this code since I'm in a similar situation with my '06. I see that your EGR was replaced a couple years prior to the P0171 so signal. Was the EGR Valve itself the only part replaced or was an aftermarket or new line and gaskets installed? Also, just wanted to see if a new module was used to connect the EGR. I have my new MAP and MAF sensors, and an aftermarket EGR Valve Kit in my garage right now and planning to start addressing this thing tomorrow! I'm getting the same DTC on my scan tool, P0171 in both banks, along with an EGR/VVT sensor stuck on 'Not Ready'. Thanks, Thomas

This is the answer: Follow the breather tube from the air duct that leads to the back side of the motor, by the fire wall. It comes out of it's hole whenever someone removes the air box cover to check the air filter. you can feel for it with your hand under the ignition coil pack to the driver side under the coil. plug it back in and reset the Check Engine Light (CEL) Here is a link that better describes it. http://www.greatautohelp.com/chevyanswers/2005-Equinox-p0171-p0496.html

I had my chevy same make. Model. Year and miles and my p0171 came on and I just replaces the hose that was attached to the pvc and it cleared my engine light. Can I still fail for that code if the engine light isn't on anymore?? Or it is cause I disconnected the battery.