Do you have 5.0 on your system yet?
If you have 5.0 this should not be possible. If you are pre-5.0, then this means you are not logged in to the TIS traffic system, or your other traffic system on board has failed. If you do not have a traffic system on board, this means you have configured a serial port to be a traffic device you do not have.
ADS-B will get some traffic without the transponder, but not much. Mostly airliners.