If your 1998 Chevrolet Blazer lost power, then its computer may have lost all memory of previously authorized remote control keyless entry fobs. If so, you must reprogram them all. If you merely bought a new fob, program all of them in this case as well. Entering the programming mode erases the computer's memory of prior authorizations as an anti-theft measure. So accumulate all the remotes, not just any new ones, to be programmed together in the same session. Only one set of instructions works for the '98 Blazer.
Close all doors in the Blazer.
Insert the ignition key without turning it.
Hold down and keep holding the unlock button in the driver's door panel with your left hand.
Turn the ignition key to "On," then "Off," then "On" and then "Off" again. Do this quickly while still holding the unlock button with your left hand. Don't turn the key so far as to turn over the engine.
Release the unlock button with your left hand. The power locks should cycle to confirm that you did it correctly. If not, remove the ignition key, open the driver's door and go back to Step 1.
Hold down the lock and unlock key on the first remote to be programmed.
Let go after the locks cycle. This should take about 30 seconds.
Repeat Steps 6 and 7 immediately for each successive remote, including any that formerly worked.
Turn the ignition key to "On" to exit the programming mode.
