What seems to be the problem and how can I fix it?

If you've already tried changing the battery in the remote, checking the fuses and relays, and disconnecting and reconnecting the car battery, and the door locks are still not responding to the remote, there are a few additional steps you can try:

Reprogramming the Remote: Sometimes, the remote needs to be reprogrammed to synchronize with the car's system. Consult the owner's manual for instructions on how to reprogram the remote for your specific model of Volkswagen Passat. If you don't have the manual, you may be able to find the instructions online or contact a Volkswagen dealership for assistance.

Check the Central Locking System: The issue may be related to the central locking system itself. Inspect the wiring and connections to ensure they are secure and not damaged. If you notice any loose connections or damaged wiring, it may require professional repair.

Faulty Door Lock Actuator: The problem could lie with the door lock actuator, which is responsible for physically locking and unlocking the doors. A malfunctioning actuator can prevent the remote from working correctly. If this is the case, the actuator may need to be replaced. It's recommended to have a qualified mechanic inspect the actuator and determine if it needs replacement.

Keyless Entry Module: In some cases, the issue may be with the keyless entry module, which receives signals from the remote and sends them to the door locks. A malfunctioning module can cause the remote to stop working. Diagnosing and replacing the module should be done by a trained technician.

If none of these steps resolve the issue, it's best to have the car inspected by a professional Volkswagen technician. They have the specialized knowledge and equipment to diagnose and repair complex electrical issues in your specific model.

Dis assemble the key FOB and perform a capacityor discharge on it.

So remove the battery, and hold the lock or un lock button for 30 seconds. Ensure the FOB battery is at 3V+, then re-assemble. Now see if it works.

If it still doesn't work, you may have to replace the FOB or re-program it. Try holding the unlock or lock button while locking the vehicle manually with the key.