GMC Chevrolet Tahoe 2003 Manual page 512

Automatic Transmission Shift Lock
Control System Check
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CAUTION:
When you are doing this inspection, the
vehicle could move suddenly. If the vehicle
moves, you or others could be injured.
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
on page 2-38 if necessary.
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 needs service.
6-14
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.
•
The key should turn to LOCK only when the
shift lever is in PARK (P).
•
The key should come out only in LOCK.