I had major issues with programming my Homelink until I cracked this code. (FYI I have 2 Chamberlain/Liftmaster 1/2HP openers).
Start by pushing the Start Button on your vehicle Without your foot on the brake to put it into accessory mode.
1. Reset all buttons on the Homelink by pushing and holding the 1st and 3rd buttons until the light on the mirror/homelink blinks red then release.
2. Assuming you are programming button 1 on the Homelink press and hold button 1, while holding button 1 hold your garage door remote within 3 inches of the mirror/Homelink and push and hold the desired button on the remote until the light on the mirror/homelink blinks fast red (it may blink slowly at first but be patient).
3. Climb a ladder and briefly push the learn button on the garage door opener head/motor (a small program light will come on). WARNING: If you hold the learn button too long you will erase the programming on the door opener head/motor.
4. Within 30 seconds hop in the car and push the desired button on the Homelink. (On my system the light on the Garage door opener head/motor blinks)
5. Test to make sure the desired button works.
6. Repeat steps 2-5 for any additional Homelink buttons you wish to program.
If you don't get the fast red blink in step 2 you may have to put a new battery into the remote.
Hopefully this solves your issues as it did mine!!!