My 2006 GX threw an uncommon code P2772 recently which according to the code reader was the L4 switch on the 4wd transfer case. It's about 60$ on EBAY and the part number is 84222-35080. You have to drop the transmission cross member to access it and I think it was a 27mm bolt size. I couldn't get an open end wrench on it so I just cut the wires and used a socket. Problem is installing the new part! I used a little silicone around the threads and used a small pair of channel locks to snug it up. Its located at the top rear drivers side of the case, way up in the trans tunnel. There are two sensors there, the forward sensor is the one you want to change out. You can test the resistance on it at the green plug below it. When it is in 4 low the resistance should be below 1 ohm and over 10k ohms when in 4 high. BTW the vehicle would occasionally not want to shift into 5th gear because of this code, hope this helps someone out there!
