"The remote is working."
Translation:Tá an cianrialtán ag obair.
My understanding is that in referring to a thing, ag obair means that it’s been prepared for use, or (depending upon the particular thing) started (“going”), and ag oibriú means that it’s functional (“working”); if that’s correct, then ag obair could be used when the remote control’s drained batteries have been replaced, and ag oibriú could be used when one is ensconced in a comfy chair, prepared to use the remote control as would be deemed necessary.
I would love to explain the specific example that made you wonder, but I can't see any lenition in this sentence, so I'm not sure what it would be.
The best I can do here is to show you the full list in GnaG, even if it may look a bit daunting: http://nualeargais.ie/gnag/lenition.htm#verwend