Truck Trend Garage: Swapping Steros in Two GMC Vehicles

Alex Steele
Sep 21, 2009
Question: I own two 2004 GM vehicles, an Impala and a Silverado pickup. The owner's manual for both states that if you move the radio from one vehicle to another, it will not work, as the radio learns the VIN of the wrong vehicle. But the Chilton repair manual for both vehicles states that if you disconnect the battery, the stereo will not work after reconnecting the battery and will read "LOC" unless you have a code. The dealer knows nothing. I need to replace batteries soon.
Photo 2/2   |   Illustrations by Steve Austin
Answer: You must have spoken to a salesman at the dealership, as any technician or service advisor should've been able to answer the question. And your Chilton manual information may be off by a year or two (factory service manuals are the way to go). GMs Theftlock (antitheft system) installed in certain pre-2003 vehicles will display "LOC" on the radio face and disable radio operation, when battery power is lost. Then a security code (included at vehicle purchase) is required to reactivate the radio. Often, vehicle owners lose the code or never receive one from a previous owner. In that situation, you can obtain the security code from a dealership, for a fee. Your 2004 Chevy car and truck are equipped with an updated Theftlock system. You no longer have to worry about the radio when disconnecting the battery. The new system does not require a security code; instead it electronically matches a partial VIN number stored in both the radio and a control module located elsewhere in the vehicle. If you remove the radio from one car and install it in another, the VIN information in the radio will not match that of the control module. The radio will then display "LOCKED" and become inoperable. The only way to have the radio's or the module's identification information reprogrammed is at the dealership, by a technician with a scan tool (Tech 2).
How To Reach Alex
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.

Can't wait for help with a problem you're having with your Truck or SUV? Ask the expert we trust here at Truck Trend Garage—visit Alex Steele at

- OF



Subscribe Today and Save up to 83%!

Subscribe Truck Trend Magazine

Subscribe to:

Truck Trend

Subscribe Diesel Power Magazine

Subscribe to:

Diesel Power

Subscribe Truckin Magazine

Subscribe to: