While I don't have any suggetions I also have a similiar problem.
Bought our 2000 Odyssey last summer. Days before Christmas check engine light came on. Took it to a mechanic, who said it was the spark plugs and had those replaced. 3 days later, light came on again. 1 month later had oxygen sensor replaced (this is what the mechanic who did the estimate says is the problem). 2 days out of the shop, less than 100 miles, light is back on. Both mechanic and auto zone say the code the second time read right for the oxygen sensor, but after having it replaced why would the light come back on?
Any ideas where to go from here?