This may have been discussed before. I recently bought a replacement key fob case from Autozone. All I really wanted was the new silicone insert, so I bought the shell or case only for about $15. Once I had everything swapped over to the new fob case I tried to establish the link. However after pouring over the threads here and a Google search session regarding how to do this, it still would not work. So I went back to the workbench and opened up the new fob. It turns out the battery side of the new fob case was not compatible with the circuit board that was in the fob I had (may have been replaced by previous owner?). The main difference being the placement of the grounding pins on the new fob case was to the center and the old one had two pins, sort of a left and right type thing. See images below)
The other issue was the new fob silicone has a different mold. The old one had undercuts that allowed for it to flex when a button was pushed. The new one fit, ut did not have the 'reliefs' in the silicone mold. Also the 'lock' part of the silicone mold would not return once pushed. The resolution to this was to clean up the old fob case (still looked good except for silicone insert), then trim some of the opening of the 'lock' with a sharp knife, sort of like deburring ever so gently. Then placed the new silicone into the old fob case with the circuit board and the program process worked the very first time.:surprise:
New case on left with old circuit board. Old case on right. Notice the single ground on the left and the double ground on the right.