Radios in Volvo vehicles sometimes come with an antitheft system that renders the radio useless unless the proper security code is entered. The antitheft system usually locks out the radio if battery power to the radio has been cut. In order to unlock the radio, you must use the radio's preset buttons to enter the security code. The problem is that you might not have the radio's security code on hand, in which case you need to contact Volvo to receive it.
Find the card that has your radio security code on it. It is a small card (around the size of a credit card) and you received it when you first bought the truck. If you cannot find the card, you can either call a Volvo dealership and request the security code or you can visit a Volvo dealership and request the security code in person.
Turn on the truck on and look at the radio's display. It should read "CODE."
Enter the radio's security code by using the preset buttons on the radio's dashboard. The radio unlocks.
If you needed to contact Volvo to request the security code, write down the code and keep it somewhere safe so you can find it if the radio is ever locked out again. You may need to provide your radio's serial number if you contact Volvo along with other personal information so they can confirm that you are the proper owner of the radio. The serial number should be displayed on the radio's dashboard.