Hi Chrism
Yes whenever disconnecting the battery over a couple of minutes, the cd player/radio will flash the word code and wont operate until the 4 digit number has been inserted.
My VX was second hand when I bought it, it was owned by queensland police prior to me, they had the 4 digit code written inside the front cover of the owners manual, it wasnt labeled as such but first time I replaced the battery I was presented with code and when looking through the owners manual came across the 4 digit number tried it and it worked
heres what the owners manual says
Radio P.I.N. (Personal Identification Number)
Your PIN. must be entered if the battery is disconnected. The P.I.N. is shown on the
security card that was originally in the glovebox of the new car. Please keep the card in
a safe but accessible place (not in your car), as this safety feature is provided as a theft
deterrent.
To enter the P.l.N.:
• turn ignition to accessories and turn radio on (“1” or “CdE 1” appears),
• press the radio buttons in your P.I.N. order,
• the radio will shortly begin to play.
If an incorrect P.I.N. is entered the number “2” or “CdE 2” appears on the display.
Following three incorrect P.l.N.s the display shows” - - - “, and the radio must remain
connected to power for approx. one hour before the correct P.I.N. can be entered.
Therefore, if your car repair requires battery disconnection you may wish to provide the
servicing dealer with your PIN.
If the P.I.N. number is lost, contact your Holden Dealer. He will require proof of
ownership and the Vehicle Identification Number shown on the inside front cover of this
handbook. There may be a nominal charge for this service.
Regards Chris