Chevrolet 1999 Blazer Owner's Manual page 397

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Brake Transmission Shift Interlock (BTSI) Check
(Automatic Transmission)
CAUTION:
When you are doing this check, the vehicle could
move suddenly. If it does, you or others could be
injured. Follow the steps below.
1. Before you start, be sure you have enough
room around the vehicle. It should be parked on a
level surface.
2. Firmly apply the parking brake (see "Parking Brake"
in the Index if necessary).
NOTE: Be ready to apply the regular brake
immediately if the vehicle begins to move.
3. With the engine off, turn the key to the RUN
position, but don't start the engine. Without applying
the regular brake, try to move the shift lever out of
PARK (P) with normal effort. If the shift lever
moves out of PARK (P), your vehicle's BTSI
needs service.
Ignition Transmission Lock Check
While parked, and with the parking brake set, try to turn
the ignition key to LOCK in each shift lever position.
D
With an automatic transmission, the key should turn
to LOCK only when the shift lever is in PARK (P).
D
With a manual transmission, the key should turn to
LOCK only when you press the key release button.
On all vehicles, the key should come out only in LOCK.
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