Chevrolet 2008 Silverado 1500 Pickup Owner's Manual page 103

For example, if the lock button and then the remote
start buttons are pressed again after the vehicle
has been running for five minutes, 10 minutes are
added, allowing the engine to run for 15 minutes.
The additional ten minutes are considered a second
remote vehicle start.
Once two remote starts, or a single remote start with
one time extension has been done, the vehicle must be
started with the key.
After the key is removed from the ignition, the vehicle
can be remote started again.
The vehicle cannot be remote started if the key is
in the ignition, the hood is not closed, or if there is
an emission control system malfunction and the
check engine light comes on.
Also, the engine will turn off during a remote vehicle
start if the coolant temperature gets too high or if the
oil pressure gets low.
Vehicles that have the remote vehicle start feature are
shipped from the factory with the remote vehicle start
system enabled. The system may be enabled or disabled
through the DIC. See "REMOTE START" under DIC
Vehicle Customization (With DIC Buttons) on page 3-76
for additional information. If your vehicle does not have
DIC buttons, see your dealer/retailer to enable or disable
the remote vehicle start system.
Remote Start Ready
If your vehicle does not have the remote vehicle start
feature, it may have the remote start ready feature.
This feature allows your dealer/retailer to add the
manufacturer's remote vehicle start feature.
See your dealer/retailer if you would like to add the
manufacturer's remote vehicle start feature to your
vehicle.
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