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The sensor is mounted somewhere on the outside of the transmission so its not like you need to take your whole transmission apart but you will need to remove a few minor things to gain access.
That trouble code refers to the Mainshaft Speed Sensor circuit. It is located on the transmission, under the battery area.
The issue can be due to the PCM, transmission, mainshaft speed sensor circuit, or an engine problem. There was a Honda service bulletin regarding it before.