If you have a car with a programmable homelink system, coupled with a car without one (using a handheld garage door opener) and possibly an keypad garage door opener attached to the outside of your garage, you know how difficult it is to program one of the devices without erasing the code on the others. I have found a secret!
We have 1 car with the Homelink built in, 2 with handheld units and a keypad outside. First you should program the handheld units. Following the directions on the main unit of the garage opener, push the program button and then hold the handheld unit up to it until the garage door moves or the main unit lights flicker or click. Test the handheld unit. If it is programmed, MOVE IT INSIDE YOUR HOME AND PUT IT INTO THE REFRIGERATOR (only for a short time.) The refrigerator acts as a shield so that the handheld unit won't be affected by programming something else. After programming all the handheld units individually (and putting them in the frig), then program your car's Homelink system using the directions in your auto's manual. After this is programmed, move your car WAAAYYYYYY down the street. Once the car is out of range, then you can go back and program your keypad on the side of your garage. At this point, everything should work. Believe me, it took me several frustrating DAYS to figure this out. Not you know the secret!