'Check brake pads' warning

[PSimmo]

This has been coming on for a week or so. Front pads have plenty of meat on them. Rears as you know dont have sensors but were replaced last year. Passenger side front sensor had been bridged out so we replaced the wire bridging in case and bridged the other side for now. Warning didnt reappear for a while longer when driving. though we'd cracked it. Warning comes on every time after 5mins or so of driving. Suggestions or similar experiances please as im taking back to my mates garage tomorrow.

Thanks