Just had the dreaded green D flashing when I had a transmission snafu, soon to be followed by a CHECK ENGINE light. My scan tool wouldn't read any codes, damn Honda, but a local shops did. With a call to the dealer for the part, he knew which switch before I told him which one, a P0847 transmission fluid pressure B circuit low, #10 on most online parts diagrams for the tranny, as well as the dealer parts guy confirming this. It was time for a tranny fluid change anyhow.
Very easy to get to the switch, in plain sight looking behind/below the battery. I was able to do a complete fluid change with a pair of needle nose plyers and a funnel and 2' of hose along with a 7/8" open end wrench for the switch.
First, drive the drivers tire up onto a stack of 2-3 2x4 boards. This will allow you to then slide, at an angle, a clear 1 gallon milk or windshield washer fluid jug, which you need to mark at a 2 quart line for reference.
Looking behind the radiator you can see 2 small transmission fluid lines going to the radiator. The drivers side line is the return line, which is easily disconnected at the upper clamp where it attaches to the tranny hard line. Put this hose into the jug which is now under the car.
Have a helper start the car while you wait and watch the fluid gently fill to the 2 quart line, then shut the car off just as it reaches 2 quarts. Leave the line in the jug to drip while you now refill 2 fresh quarts of tranny fluid thru the quite large tranny dipstick hole, with the funnel and hose.
Now go back to your dirty oil container, remove from under the car and dump it all out for recycling into another container. Replete this procedure 2 more times and you will have swapped out the trannies 6.18 quart fluid capacity.
Start to finish, this method took me a whole 15 minutes, and then another 5 minutes to swap the switch.