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Have you tried a different key? If nothing is working, the tumbler may have gone bad and need replaced. Have you tried to see if a small amount of lubricant helps?
If nothing is helping, you will need to remove the tumbler and see what is happening. Most likely, the tumblers in the lock assembly have worn out or broken.
Here are the directions for replacement. The attached pics correlate with the directions. I'm not 100% sure, but the new key may require programming. There is nothing listed in the manual, but I swear it was required.
2005 Chevy Truck Tahoe 4WD V8-5.3L VIN T
Ignition Lock Cylinder
Vehicle Steering and Suspension Steering Steering Column Service and Repair Removal and Replacement Ignition Lock Cylinder
IGNITION LOCK CYLINDER
Ignition Lock Cylinder Replacement
1. Disconnect the negative battery cable.
Caution: Refer to SIR Caution in the Preface section.
2. Disable the SIR system.
3. Lower the knee bolster.
4. Remove the steering column trim covers.
5. Use the key in order to turn the ignition lock cylinder to the START position.
6. Install an allen wrench into the hole on the top of the lock cylinder housing.
Push down on the allen wrench in order to release the tab on the lock cylinder inside the lock cylinder housing.
7. Slide the lock cylinder out of the lock cylinder housing.
Important: The gears between the ignition switch and the lock cylinder housing must be in the correct position. Failure to do so will cause a misalignment of the gears in the ignition switch and the lock cylinder housing, which may result in a NO START or BATTERY DRAIN.
1. Use a screwdriver in order to rotate the lock cylinder housing gear clockwise to the START position.
2. Remove the screwdriver and allow the lock cylinder housing gear to spring return to the RUN position.
3. Install the key to the lock cylinder.
4. Align and install the lock cylinder to the lock cylinder housing.
5. Install the steering column trim covers. Refer to Steering Column Trim Cover Replacement.
6. Install the knee bolster.
7. Enable the SIR system.
8. Connect the negative battery cable.
Let me know if this helps or if you have other questions.
Images (Click to enlarge)
Monday, October 14th, 2019 AT 8:02 PM