I have a 2008 HHR and the radio showed locked. I tried the wikihow instructions but had no luck unlocking it (couldn't get to the time adjustment to enter the code)and my dealer wanted $49 to unlock it. I pulled the fuse for audio, plugged it back in, I have tunes again.

 

Why did it show "locked". Was it because the battery had died or because the radio was replaced with a junkyard radio?

 

I had to jump the battery in January and once again in March. In April, the "Locked" appeared on the radio. I checked the battery and it was still good, just not fully charged. I charged it fully but still had no luck until yesterday when I decided to pull the fuse.

 

The contents security system is activated when the battery dies, that is the reason your solution worked.

This is a different case, when you try to install a used radio the numbers need to be negotiated. A "brand new" GM radio made for the car model will do the negotiation automatically. A used radio needs to have data changed. It is a matter of data matching.

12V is a dead battery, the security gets triggered somewhere around 9V.

 

Pulling the fuse , effectively is a mini battery lobotomy to the radio, a reboot of sorts.

 

I think I need a lobotomy for keeping this car for 10 years! First 6-8 not so bad, last few years it is one thing after another. Hard to complain about 180K miles, though.

 

I’m at 267,000 still going strong. Most mileage I ever got out of a 4 cylinder car.