Get and AM Radio, tuned off station.
Then with a good battery installed in one of the door buttons.
Hold it close by the AM Radio.
Press the button, and listen for the RF noise from the transmitter.
If you got some kind of noise.
Then you know it is transmitting.
So, as haklesup said:
If a component has drifted and shifted the signal, it may be deaf at the receiver to its calls.
Signed: Janitor Tzap