Officials say they are investigating a fault which meant new flood warning signs did not alert motorists to flooding in Wensleydale yesterday.
The signs were installed on the A684 last year at a cost of £418,000 to warn motorists that the road was flooded with water from the River Ure.
Several stretches of the road are prone to flooding, including parts near Wensley and between Aysgarth and Worton.
Local residents say the signs failed to illuminate yesterday despite flooding near Worton Bottoms.
It was claimed the reason was that sensors that detect river water levels were placed in the wrong place.
This was rejected however by county council bosses.
North Yorkshire County Council’s corporate director for business and environmental services, Karl Battersby, said: “Since its installation early last year, the flood detection system on the A684 has been very effective in highlighting floods and has generated positive feedback from local communities and regular users of the route.
“There is no suggestion that the sensors may be in the wrong location. For each sign there are several sensors, including near the river as well as near the road so it is highly unlikely they could all fail.
“We are aware of a fault in the Aysgarth area today resulting in the sign not illuminating. We have reported the problem and engineers are currently investigating the fault.”