It could be in the owner manual.
what the hell are you talking about.
Code for WHAT
honda odyssey
Likely your transmission is dying. Google "odyssey transmission" and you will find lots of reports about problems with 2000- 2004 Odyssey transmissions. If you are persistent enough, Honda might help some with the repair.
To reset the code in a 2006 Honda Odyssey after changing the battery, you typically need to enter the radio or anti-theft code. First, turn on the ignition without starting the engine. Then, if the radio displays "Code," enter the correct code using the preset buttons. If you don't have the code, you can find it in the owner’s manual or by contacting a Honda dealer with your vehicle's VIN.
found at http://www.freeebookpdfmanual.com/car/honda-car/2008-honda-odyssey-owners-manual/ but that 2008
The 2001 Honda Odyssey EGR valve is located on the outside of the air cleaner housing. You will find the valve, on the back of the housing.
Push at radio #1and #6 at same time when turning ignition on and will show code and input code(you may find it in glove box sticker 5 or6 numbersand press those numbers and will unlock radio. That may not work, so if it does not, go to the Honda Owners Link, sign up, and you can get the code if the radio is an OEM unit. Click the link.
There are many different sources to find a used car such as a Honda odyssey. Newspaper ads, websites and even tv commercials can give you insight on the best location to find what you are looking for.
I do not know what you mean by decode. If you are wanting to know what the code is for your 2000 Accord it is easy to find out. Just go register your Honda at the Honda Owners Link I will provide. Once you register the car you can get the radio code there for free by simply asking. Click the link and sign up.
Read your owner's manual. Your answer can be found there. But you will find the answer is not there.
This could mean many things such as an oil replacement to a transmission problem. Take the car to a shop for close inspection, and they should find the problem.