A 2014 Ford Focus estate had lost remote lock and unlock and would not keylessly start. Batteries had already been changed without success. The useful question was not “what part can we try?” but “which part of the keyless chain is failing?”
One result, then another clue
Ford-specific software restored the remote functions, but the vehicle still required the emergency slot to start. That partial success narrowed the problem: communication had improved, but the key was not yet behaving correctly for keyless start.
Systematic key diagnosis
Further key diagnosis and repair restored keyless operation. Each stage was verified before moving on, keeping programming, vehicle-side and key-side possibilities separate.
The lesson
When replacement batteries do nothing, a keyless fault may need software, communication and key hardware checked as one system. Partial improvement is evidence—not the end of the diagnosis.