Critical moment taking in probe that's malfunctioning (8,5)
I believe the answer is:
breaking point
'critical moment' is the definition.
(both can mean an important or crucial moment)
'taking in probe that's malfunctioning' is the wordplay.
'that's malfunctioning' indicates an anagram.
'taking'+'in'+'probe'='takinginprobe'
'takinginprobe' with letters rearranged gives 'BREAKING-POINT'.
(Other definitions for breaking point that I've seen before include "Moment at which something gives way" , "The end of one's tether?" , "Critical moment for collapse" .)