2024 Honda Odyssey 22k miles w/ U0100 error code but no dash lights. Dealership wants $230 diagnostic fee

Just bought a 2024 Honda Odyssey CPO (still under bumper-to-bumper warranty). Ran my Xtool OBD2 scanner and found code U0100, but the check engine light is NOT on. Dealer says it's a $230 diagnostic fee if they find the cause isn't covered by the warranty. Given that it's a CPO, how should I handle this?