Originally Posted by S-Runner '01
You say "Get it checked out." Kinda makes you sound like a Toyota dealer wanting me to "Get it checked out."
I'm trying to check it out by posting here. Do you have an answer to my question?
I did answer your question. Anything you are told on here, for that code, will be a guess. A P0171 code is set when the vehicle has reached adaptive limits for fuel control. It has added fuel to the base table until it is outside an accepted range. There can be several reasons for this. It would depend on what the fuel trims are under different driving conditions. Where the trims are out of range is the first clue to the root cause and can only be seen on a test drive with the correct equipment. Then some tests to verify the root cause and then the repair. If you toss a part at it that is a couple hundred dollars and it does not fix it, "checking it out" would be the cheaper route.
I am not a Toyota dealer or a Toyota tech. I am a CMATL1 certified technician and an automotive diagnostics instructor.
Sorry my answer did not fit your expectations. Guess away. Could be as simple as a clogged fuel filter, a tank of gas with a high ethanol content or as expensive as an AFR sensor or failed MAF. Pick a starting place and spend away. You said it was under high load (climbing a hill on the highway) so start with the items that would be important under those conditions.