This will work for all 2002 and up CRV's. Older models may need to have the radio removed to get the serial number.

Radio Code Retrieval.

Turn the ignition switch to ON.
Turn ON the device and confirm that the display reads COdE. If you don’t see this message, pull the backup fuse for 1 minute, and then go back to step 1.
Turn OFF the device.
Press and hold the 1 and 6 radio preset buttons, and turn ON the device.
The display toggles between two screens: U with the first 4 digits of the serial number (U2200 for example,)
And L with the last 4 digits of the serial number (L0055 for example.)
Ignore the U and L and record all 8 digits

Once you have the radio serial number contact your local dealer.

United States Residents can use this link and insert the required information.