I have a 2018 Honda Odyssey with 30k miles. The following warning just popped up on the dash, "Collision Mitigation System Problem", and the "Brake System" light is illuminated.
How do I begin to go about trouble shooting this? There are no trouble codes present (per the Bluedriver scan tool).
I had this problem on my 2018 Odyssey EX-L and took it to the Honda dealer to have them reset everything and I haven't seen the issue since, happened last summer probably 3 or 4 thousand miles back. They weren't 100% sure what caused it but they said it may have been related to when I accidentally let the battery drain when cleaning/detailing it, I had to use jumper cables to get it to start. On a side note, I was a little surprised that the battery drained, I didn't have the car on just the doors open and I thought there were auto off features that shut everything down after 20 minutes or so to prevent battery drain but that apparently didn't work in that instance.
Very complicated systems commonly have issues on first year of newer generations. I would bring it to Honda like you did.
I brought it to the dealer, and the cause was "u128d found". Battery was weak, should be 620 CCA and was only 354 CCA. The dealer replaced the battery with a new one, and it appears to be fixed.