Chevrolet 2003 Astro Owner's Manual page 173

Activating the Theft-Deterrent Feature
The instructions which follow explain how to enter your
secret code to activate the THEFTLOCK@ system. Read
through all nine steps before starting the procedure.
If you allow more than 15 seconds to elapse between
any steps, the radio automatically reverts to time
and you must start the procedure over at Step 4.
1. Write down any three or four-digit number from
000 to 1999 and keep it in a safe place separate
from the vehicle.
2. Turn the ignition on.
3. Turn the radio off.
4. Press the 1 and 4 pushbuttons at the same time.
Hold them down until
- -
- shows on the display.
Next you will use the secret code number which you
have written down.
5. Press MN and 000 will appear on the display.
6. Press MN again to make the last two digits agree
with your code.
7. Press HR to make the first one or two digits agree
with your code.
8. Press AM FM after you have confirmed that the
code matches the secret code you have written
down. The display will show REP to let you know
that you need to repeat Steps 5 through 7 to confirm
your secret code.
9. Press AM FM and this time the display will show
SEC to let you know that your radio is secure.
The LED indicator by the volume knob will begin
flashing when the ignition is turned off.
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