Both these codes indicate a probable leak in the evaporative emissions control plumbing for the fuel tank. The codes are likely due to a failure of the evap system autotest, which runs some number of hours after the engine was last run and fuel tank temperature has stabilized (typically in the middle of the night.)Quick update - tested it out last night, put in 5 gallons, transferred it to the main. All went through smooth. Burned some of the fuel, added 10 more gallons, then transferred it. All went well and it filled the main. Started the vehicle this morning and had CEL and TRAC OFF illuminated. Pulled the codes and got P0441 and P0455. These imply something is wrong with the EVAP (charcoal canister) system. I checked and everything looks good from a hose connection perspective, so I'm wondering if it's an issue with the gas cap. I pulled it, tightened it down and cleared the codes. I'm all ears for anyone else that may have experienced these issues. Let's hope it doesn't return!
There is a Toyota Repair Manual Supplement (EG-048-04) that covers the operation of the evap system, and provides troubleshooting help. This is based on the use of Toyota diagnostic tools, but if you can rig a manometer or Magnehelic gage capable of measuring inches-of-water-column pressure levels, you can probably follow the fault tree.
Below is one of the illustrations from this Supplement showing system pressure at various times, relative to solenoid states, and where a P0455 "gross leak" might be detected when there is a vacuum leak of ambient air into the evap system.
Here is the link to the complete document:
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