Sounds like a short since water is involved so perhaps skip down to the electrical part of the list first?
FSM says about 0440 possible causes in easy to check order:
Hose or tube cracked, holed, damaged or loose seal ((3) in Fig. 1)
Fuel tank cap incorrectly installed
Fuel tank cap cracked or damaged
Vacuum hose cracked, holed, blocked, damaged or disconnected ((1) or (2) in Fig. 1)
Fuel tank cracked, holed or damaged
Charcoal canister cracked, holed or damaged
Electrical stuff starts here:
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
ECM
Or the code can just be reset after a heavy rain.
Luck and enjoy the Runner.
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2001 Limited 4WD - 346+K - SunfireRed\Thunder Cloud; - 265/75/16 Michelin A/T2s - Fat Pat's 1.5" BL - StopTech ANGLED rotors - In series 699 trans cooler, New Yota1 transmission, All new OEM suspension front to rear.