Chevrolet 2008 Colorado Owner's Manual page 102

If you have an automatic transmission, the ignition
switch cannot be turned to LOCK/OFF unless the shift
lever is in PARK (P).
If the steering wheel is locked, move it from right to left
and turn the key to ACC/ACCESSORY. If none of
this works, then your vehicle needs service.
(B) ACC/ACCESSORY: This is the position in which
you can operate your electrical accessories or items
plugged into the accessory power outlets. On automatic
transmission vehicles, this position unlocks the ignition.
On manual transmission vehicles, it unlocks the ignition
and steering wheel. Use this position if your vehicle must
be pushed or towed.
(C) ON/RUN: This is the position that the switch returns
to after you start your engine and release the switch. The
switch stays in ON when the engine is running. But even
when the engine is not running, you can use ON/RUN to
operate the electrical accessories and to display some
instrument panel cluster warning and indicator lights.
The transmission is also unlocked in this position on
automatic transmission vehicles.
2-20
The battery could be drained if you leave the key in the
ACC/ACCESORY or ON/RUN position with the engine
off. You may not be able to start your vehicle if the battery
is allowed to drain for an extended period of time.
START (D): This is the position that starts the engine.
When the engine starts, release the key. The ignition
switch returns to ON/RUN for driving.
When the engine is not running, ACC/ACCESSORY
and ON/RUN allows you to operate the electrical
accessories, such as the radio or items plugged
into the accessory power outlets.
A warning tone will sound if you open the driver's
door when the ignition is in ACC/ACCESSORY or
LOCK/OFF and the key is in the ignition.