GMC 1996 Savana Van Owner's Manual page 142

If the code entered is incorrect, SEC will appear on the
display.
The radio
will remain secured ~ ~ n t i l the correct
code is entered.
When battery power is disconnected from a secured
radio, the radio won't turn on and LOC will appear on
the display.
To unlock a secured radio, see "Unlocking the
Theft-Deterrent Feature After a Power Loss" earlier in
this section.
Understanding Radio Reception
FM Stereo
FM stereo will give you the best sound. But FM signals
will reach only about 10 to 40 miles (16 to 65 km). Tall
buildings or hills can interfere with FM signals, causing
the sound
t o
come and go.
AM
The range for most AM stations is greater than for FM,
especially
at
night. The longer range, however, can
cause stations to interfere with each other. AM can pick
up noise from things like storms and power lines. Try
reducing the treble to reduce this noise if you ever get it.
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