It's under the radio, but it can be accessed without removing the radio. Move the carpet out from where the dash and center console meet, by your feet. You should be able to move the carpet out of the way without removing anything. You can get to the monitor there. It's a blue box permanently mounted to its bracket.
The code 61 means "Intermittent or Repaired Diagnostic Monitor Not Mounted to Vehicle Properly". You probably know that, but I'm posting it for anyone else whose reading this thread. The monitor grounds itself through the frame, so it basically has a bad ground. Clean the mounting points, and make sure the screws are tight.