When I hit the Unlock button on my keypad, it only opens the driver's door. When I use the Unlock button inside the car, all 4 doors open with no problem.

Locking mechanisms are obviously working. Sounds like an electrical problem. The keypad is designed to open the driver's door on the first push, and then open all the doors on the second push. It's not doing the second part.

Could it be the keypad, or more likely something inside the car?

Thanks.