GMC SIERRA 2020 Owner's Manual page 251

250 Driving and Operating
Alerting the Driver
With Head-Up Display
Without Head-Up Display
If ACC is engaged, driver action
may be required when ACC cannot
apply sufficient braking because of
approaching a vehicle too rapidly.
When this condition occurs, six red
lights will flash on the windshield.
Either eight beeps will sound from
the front, or both sides of the Safety
Alert Seat will pulse five times. See
Collision/Detection Systems under
Vehicle Personalization 0 156.
See Defensive Driving 0 187.
Approaching and Following a
Vehicle
The vehicle ahead indicator is in the
instrument cluster. It only displays
when a vehicle is detected in your
vehicle s path moving in the same
direction. If this symbol is not
displaying, ACC will not respond to
or brake for vehicles ahead.
ACC automatically slows the vehicle
down and adjusts vehicle speed to
follow a detected vehicle ahead at
the selected following gap. The
vehicle speed increases or
decreases to follow a detected
vehicle in front of your vehicle when
that vehicle is traveling slower than
your vehicle set speed. It may apply
limited braking, if necessary. When
braking is active, the brake lamps
will come on. The automatic braking
may feel or sound different than if
the brakes were applied manually.
This is normal.
Stationary or Very Slow-Moving
Objects
Warning
ACC may not detect and react to
stopped or slow-moving vehicles
ahead of you. For example, the
system may not brake for a
vehicle it has never detected
moving. This can occur in
stop-and-go traffic or when a
vehicle suddenly appears due to
a vehicle ahead changing lanes.
Your vehicle may not stop and
could cause a crash. Use caution
when using ACC. Your complete
attention is always required while
driving and you should be ready
to take action and apply the
brakes.