If you've recently changed your car battery or had a repair, you might find your radio asking for a 4-digit security code
Once you have your Pre-Code, you can generate the final unlock code: Free Apps:
Converts a 4-digit pre-code (typically one letter followed by three numbers, such as "S313") into the unique radio unlock code.
On many models, press and hold buttons 1 and 6 simultaneously. The pre-code should flash on the radio display.
"You could pull the radio out and call the dealer with the serial number," Sarah said, "but there’s an easier way. Have you heard of a ?"