Vauxhall Radios - radio works normally after entering code but display doesn't work

This often happens when a radio belonging to a car with a larger display (10 segment) is fitted to one typically with a small centre console display (8 segment). e.g. transferring the radio from a Vectra to a Corsa.

The CAR300, CAR400 and CDR500 can support both display types but it needs to be told which display type to use.

Here is how is done on a CDR500:

With the car ignition on, press and hold buttons 3 and 5 together and switch on the radio whereupon it will show either DISPLAY 8 or DISPLAY 10. Keep the buttons pressed until the radio beeps and the display will change from 8 to 10 or vice versa.

Release the buttons, switch the radio off and then back on and hopefully the radio will now operate correctly with your display.

Here is a list of buttons to hold in on other models

Keys used to toggle display mode  
Make Buttons 
CAR300 4 + 6 
CAR400  4 + 5 
CDR500  3 + 5