If there's nothing in the Fiat owners manual, I copied these from Suzuki SX4 pdf manual. One of these two methods may work, but no promises...
Method 1.
To program a new transmitter
1) Confirm that all the doors are closed and the ignition key is out of the ignition switch.
2) Open the driver’s door.
3) Insert the key, turn the ignition switch to the “ON” position, turn the ignition switch to the “LOCK” position and remove the key within 10 seconds.
4) Push and release the driver’s door switch (interior light switch located on B pillar) 3 times, insert the key, and turn the ignition switch to the “ON” position within 20 seconds.
5) Turn the ignition switch to the “LOCK” position and remove the key within 10 seconds. All doors will lock/unlock to confirm that this procedure has been properly completed.
6) Press the “UNLOCK” button on the transmitter one time within 20 seconds (after step 5). All the doors will lock/unlock to confirm that the procedure has been completed and the transmitter has been programmed.
7) If you want to program an additional transmitter, repeat the procedure from step 1) through step 6).
8) Make sure that the keyless entry system operates properly by operating each transmitter.
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Method 2.
To program a new remote controller
1) Close all the doors of the vehicle.
2) Sit in the driver’s seat and confirm that the driver’s door is unlocked.
3) Insert the key into the ignition switch.
4) Complete steps 1 through 6 described below within 25 seconds after step 3).
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1. Push the power door locking switch of the driver’s door to the lock position and then push it to the unlock position.
2. Repeat step 1 two more times.
3. Push the power door locking switch of the driver’s door to the lock position.
4. Remove the key from the ignition switch and then insert it again.
5. Repeat step 4 three more times.
6. To start the engine, turn the ignition switch to the “START” position.
Wait for 3 seconds.
7. Proceed to step 5) within 60 seconds after the engine has started.
NOTE:
You cannot program the remote controller if you don’t complete steps 1 through 6 within 25 seconds.
You cannot program the remote controller if you do not proceed to step 5) within 60 seconds after the engine has started.
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5) Turn the ignition switch to the “LOCK” position.
A buzzer will sound twice and the door lock switch will be activated from the lock position to the unlock position automatically.
6) Press the “LOCK”, “UNLOCK” or “PANIC” button on the remote control-ler.
A buzzer will sound twice and the door lock switch will be activated from the lock position to the unlock position automatically.
If you want to program an additional remote controller, repeat the procedure of step 6) using the additional remote controller.
NOTE:
Complete step 6) within 30 seconds.
You can program up to four remote controllers.
7) To complete programming, remove the key from the ignition switch or turn the ignition switch to the “ON” position.
8) Make sure that the keyless start system and keyless entry system operate properly by operating each remote controller.
If you cannot operate the keyless start system and/or keyless entry system, repeat this programming procedure again.
