The only Code to look for is "3". That's the transmission fluid service minder. "B" just means Oil and filter change with a multi-point inspection.The user's manual says "don't do it yourself."
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I'm sure some DIY'ers are qualified to do it, but to me this says "If you don't already know, you aren't one of them." I know I'm not, so I haven't bothered to look for how to do it.
That said, the schedule is "watch the maintenance minder for code B3." There is a disclaimer in the manual that says if you drive at low speeds in mountainous regions, do it at 47,500 miles or 3 years. That probably puts a reasonable interval for normal usage at around 60,000 miles, which I have seen advertised by Honda dealers.
Each person will have a different driving profile. Make sure to follow the minder when it prompts. The only exception is mountainous areas because it puts more strain on the trans and the algorithm has no way of knowing altitude changes.
Consequently, I would not have aided anyone in goodwill cases had they never changed the trans fluid and had trans issues after 60k miles. The dealer can't tell when it prompted you for a fluid change and you skipped it. General rule of thumb was that it would have prompted by around 60k miles at least once.
Also, side note... The 10 speeds shouldn't need fluid changes every 30k miles. A Honda engineer actually told me it would be closer to 100k miles in normal driving conditions. But, again... see above.