The P171 System lean bank 1 means too much air, not enough fuel, usually caused by a dirty or bad Mass Airflow Sensor, the trapezoidal part on the big air
Intake hose right behind the
Air Filter box, held down by 2 small philip screws.
Swap in a known good MAF sensor from another Toyota or Lexus to see if that fix the problem. All Toyotas and Lexus use the same MAF made by Denso. If that solves your problem then replace with a new MAF, or clean the old one with non-residue contact cleaner spray sold in Walmart.
if that did not fix the problem then there may be air leaks on air hoses or vacuum lines around the throttle body or the airbox. If one of those little black rubber hoses are not hooked up tight or cracked, it will pull the P171 code.
The 400s codes have to do with the evaporative system, recirculating gas vapor from the charcoal canister on top of the gas tank to the throttle body for burning. After 150K miles, the canister is likely broken, not holding gas vapor and needs to be replaced.
At 250K miles, my GTS had those codes. I bought an used canister on eBay for $100. It came with a solenoid, switch and hoses. One hour labor $80 to install and those codes were fixed. The car would have to be on a lift for access to the gas tank. It's not convenient or safe to get under the car on jack stands.
