While slowly backing into a parking space in an underground hotel garage, the rear parking sensors never activated — no audible warning at any point — and the vehicle's left-rear corner struck a concrete wall corner, cracking the taillight and damaging the bumper/quarter panel (~$3,000 repair). Sensors function normally at all other times; this was an intermittent non-activation. Rear dashcam with cabin audio documents the backup with no sensor tones before impact. No injuries.