I am going to trade in my volvo s40 after taking out my aftermarket radio and putting back the stock radio it asks for a code. I can't find the code in my manual guessing previous owner still has it. I was wondering if someone knew how to find the code using my serial number or if there was an override for the radio.

You have to call a Volvo dealership and give them your VIN# and they will provide the radio code to you free of charge.