Have you connected all the wires to the radio?
Using one of the wires, the radio asks the car's unique number via the CAN BUS system.
If the number does not match one that the radio has stored during its first power-up OR if the radio cannot get any information - the anti-theft feature activates.
Some of the radios will allow to enter the anti-theft code if they CAN get the number but it does not match (that's why I'm asking about the wires).
Some of the radios will just show 'CANCHECK' and will not allow any entry.
A.R.S., December 2012