Programming replacement keyless entry transmitter

I have successfully programmed a new original factory replacement transmitter for a 1997 Chevy Cavalier, which is working fine, however in the process my 2 existing transmitters are no longer functional and unable to be programmed despite following all instructions on numerous repeated attempts. Any thoughts???

Since you can program the new transmitter you are obviously entering program mode. Were the two transmitters that cant be programned working fine before? You just wanted to add one? Try doing one of the originals back. Are you grounding a wire in the trunk to get in programn mode (confirmed by power lock cycling) or are you working with a connection in the data link connector?It is normal to loose function in previously functioning remotes as soon as you enter program mode all remotes must be programed in the same programing session.

With my car, not a GM vehicle, if you program one, you have to program all of them. The programming procedure is essentially a reset and you start all over with all the remote as oldschool indicated.

You need to do all of them at the same time, quickly

Of the two original transmitters that can’t be programed, one was working perfectly fine while the other was able to unlock doors yet unable to unlock the trunk, which was the reason I bought a new replacement!!! We were grounding a wire in the trunk to get in program mode amd repeatedly attempted to program all 3 in the same programming session. Any additional thoughts?? Thank you for your interest.