When you vehicle was shipped from the factory it was programmed in Mode 1. To change to a different mode, do the following:

1. Put tranny into PARK for Auto's or REVERSE for Manuals with the parking brake engaged and turn the ignition ON.

2. Press and hold the lower part of the power door lock switch for 10 seconds. Release the switch when you hear the chime.

3. Count the number of chimes you hear. The number of chimes tells you which mode your vehicle is in. You can change what mode your in by pressing and holding the lower part of the power door lock switch (two chimes for Mode 2, three chimes for Mode 3 and four chimes for Mode 4).

4. Repeat Step 2 until you hear the number of chimes that matches the mode you want.

The Modes:

Mode 1:
All doors automaticall lock when shifting out of PARK. The doors will remain locked unless manually unlocked or the lock button is pressed. All doors will unlock when you shift back into PARK and the ignition is turned OFF.

Mode 2:
This mode is only available on vehicles with a remote keyless entry. All doors automatically lock when you shift out of PARK. Automatic drivers door only unlock when shifting back into PARK and the ignition is turned OFF.

Mode 3:
All doors automatically lock when you shift out of PARK. No automatic door unlock.

Mode 4:
No automatic door lock or unlock.

These modes are the same for the manual transmission, just use "REVERSE" in the instructions in the place of "PARK" and the lock occurs when you reach 5-mph.

Also I am not sure if you will hear the chimes if you have an aftermarket stereo, unless you relocated your factory stereo. Any know?

You'll be able to just fine on a '99, since you don't have to deal with relocating your stocker or anything to hear chimes.