The 84-year-old from the southern town of Bad Bocklet in Lower Franconia had planned to take his car to the nearby testing centre down the road on Tuesday afternoon.
But many wrong turns and 20 hours later, he found himself in Hesse on Wednesday lunchtime.
Police said they discovered the man after he made repeated driving errors on his convoluted journey through Bavaria, Hesse and Lower Saxony.
A squad car finally stopped the man as he drove through the central German city of Kassel, where he was taken to a clinic for checks.
Police said he only narrowly avoided causing an accident on his drive through three German states.
Officers said in a statement that the man caught their attention through his erratic driving and they suspected him of drink driving.
“It was quickly determined that the pensioner, while sober, was completely disoriented,” Kassel police said in a statement.
They added there was “considerable doubt” that the man would be fit to drive in the future.