Speaking to the Radio Times, the programme's mechanic Guy Bostock explained that he has struggled to find the parts he needs because viewers have bought them.
He also revealed that he tried to buy a second car at the start of the season and discovered that the price had doubled.
An source said: "Supplying an Audi Quattro should have been easy, yet Bostock has found replacement parts difficult to source."
On the show, Gene Hunt (Philip Glenister) owns one of the vehicles and often says: "Fire up the Quattro."
Ashes To Ashes continues on Friday at 9pm on BBC One.