2008 GMC Envoy Remote Programming Procedure:
IMPORTANT: Before entering programming mode, have in-hand every fob you will be using on the vehicle, including old ones you want to keep working. Once you program the transmitter, all previous codes will be eliminated from the memory. The other transmitters will not be functional until you program the transmitters again.
1. Shut all car doors, have windows closed, wait for dome light to turn off.
2. Insert the key into the ignition.
3. Press and Hold the power UNLOCK button on the driver’s door panel-don't let go until step 9.
4. Do steps 5 to 8 very fast.
5. Move the ignition switch to the ON position (as far as you can go WITHOUT cranking the engine).
6. Turn the ignition switch to the OFF position.
7. Turn the ignition switch to the ON position.
8. Flip the ignition switch to the OFF position.
9. Release the power unlock button on the door panel. The car will lock and unlock the doors by itself.
10. Hold down the LOCK and UNLOCK buttons on the transmitter together until the door locks lock and unlock. This step may take up to Half a minute.
11. Repeat step 10 for each additional keyfob(including any existing fobs).
12. Rotate the ignition switch to the ON position in order to depart the keyfob learning method.