Nearly 40 vehicles were stopped in a police operation this week.
Two motorists were fined and seven others were ordered to look at faults with their vehicles during a five-hour clampdown in Fakenham on Monday.
A police spokesman said that officers had stopped 37 cars and vans travelling along the A148, in a joint operation with HM Revenue and Customs and the Vehicle and Operational Services Agency (VOSA).
One of the vehicles which was stopped was found to be illegally using red diesel. Its driver was fined £530.
Meanwhile, VOSA issued seven prohibitions for various faults on tyres, suspension and brakes.
Police also issued one fixed penalty notice for driving otherwise than in accordance with a licence and also gave a verbal warning.