The actress, who was represented by solicitor Nick "Mr Loophole" Freeman, entered the plea when she appeared at Macclesfield Magistrates' Court.
Knox , who plays Rita Tanner in the ITV soap, was charged following an incident in Knutsford, Cheshire, on March 10.
The 80-year-old was said to have been a passenger in a Jaguar vehicle driven by her daughter, Maxine Ashcroft, 56.
The car was stopped by police after a member of the public reported they thought the driver was under the influence of alcohol.
Ashcroft was found to be nearly three times over the legal limit when she gave a breathalyser reading at Middlewich police station.
The veteran actress later arrived at the station and was arrested herself on suspicion of drink driving. A sample of her blood was taken which gave a alcohol reading of 85 micrograms per 100 milliletres of blood - the legal limit being 80.
She was bailed pending further inquiries and charged on April 4.
Ashcroft, from Lechlade, Gloucestershire, was banned from driving for two years in a hearing at the same court earlier this month.