If this is Factory Ford Keyless Entry..
Standing next to vehicle "Press & Hold" the Lock & Unlock Buttons "together" for apprx 10 seconds
Release Buttons & try remote
If the above does not work, you may need to Program Transmitters again, by following the procedure below or use of Dealer Scan tool to Master code
REMOTE KEYLESS ENTRY TRANSMITTER PROGRAMMING
CAUTION: All remote keyless entry (RKE) transmitters must be programmed at the same time.
The vehicle must be electronically unlocked before entering program mode (via RKE, RKE keypad (if equipped) or door lock control switch while the driver door is open.
Turn the key from OFF to RUN 8 times within 10 seconds , with the eighth turn ending in RUN. If the module has successfully entered program mode, it will lock and then unlock all doors.
Within 20 seconds , press any button on an RKE transmitter, and the doors will lock and then unlock to confirm that each RKE transmitter has been programmed.
Repeat this step for each RKE transmitter.
If the door locks do not respond for any RKE transmitter, wait several seconds and press the button again.
If the door locks still fail to respond, refer to Inspection and Verification.
Make sure that no more than the maximum number of RKE transmitters are attempted to be programmed.
Exiting the programming mode is accomplished if one of the following occurs:
The key transitions to the OFF position.
20 seconds have passed since entering programming mode or since the last RKE transmitter was programmed.
The maximum number of RKE transmitters have been programmed.
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