I recently bought a used 2003 Chevy 2500 w/Duramax/Allison etc.
I want to start sound deadening to make it a more pleasant family vehicle and have it easier on my screwed up ears. A good place to start is the doors, but Haynes says it's necessary to disconnect the negative terminal from the battery (batteries on the Duramax).

If I was not supplied with the secret code for the stereo, how the heck can I perform this function without creating other problems?

Also, what other things should I be concerned with when disconnecting both batteries on the Duramax?

Which one first?

Is the battery on the right rear only used in starting the engine?

Thanks!

I am not sure that the 03's had the Theftlock. I know that is the year GM refreashed the interiors though. If your radio looks like the first pic supplied and has the blinking red light next the the volume, then it has a code stored. If you have that radio and the red light is not blinking, then it has no code stored. If your radio resembles the second pic, then I belive it looks at your VIN to lock unlock it and you won't need to install a code once powered back up. On the battery question, they are hooked up in parallel so the help each other out. They are not assigned to a specific function. They are more for the glow plugs than anything.

I had both batteries disconnected on my truck (2003 2500HD D/A Crew) for at least an hour and the radio worked just fine, are you sure it has a security code? I didn't even lose my presets. Mine has the 1-CD Bose system, in case that matters or yours is different. Good luck.

no security code on the 03+ trucks. Try disconnecting the batteries, otherwise you will have to go to the dealer.

ben

I have the radio on the right! So, right on!
Any other things I should look for when disconnecting the batteries?