Your 1999 Tahoe may be equipped with GM's Vehicle Anti Theft System or VATS. The VATS system is composed of a set of contatcs integrated into the ignition carrier, which reads the unique resistance value of a resistor embedded within the key.
When you attempt to start the vehicle the Tahoe's VATS module reads the resistance value from the key. If it does not match the programmed value the VATS module will command the Powertrain Control Module (PCM) to disable the injectors and the spark system.
If you change out your ignition tumbler, you will have to use the new keys, which contain different resistance values! This will prevent your Tahoe from starting.
But all hope is not lost. The most expensive and easiest option would be to have a dealer change out the ignition and use their Tech2 tool to reprogram the VATS module to the new keys. This takes less than 10 minutes.
The cheaper and more time-consuming option is to attempt to use the owner key re-learn procedure. The steps are as follows.
- Replace the ignition tumbler.
- Turn the ignition on with the new key & move key up to start returning to run.
- Wait 10 minutes, At this time the Security light will flash, until the end of the 10 minute period at which the Security light will stay on for 3 seconds then turn off.
- Turn key back to Off position and wait 5 seconds.
- Repeat Step 1-2 three more times. On the fourth time the Security light will turn off and not come back on. SUCCESS!
- Attempt to start normally.
- Repeat entire procedure for second key.
Good luck! Keep us posted.