What "No Key Detected" actually means.
The vehicle is sending an LF (low-frequency) challenge to the fob and is not receiving a valid response. That can be caused by any of the following:
- Dead or weak fob battery — even on proximity fobs used without pressing buttons, LF response requires power.
- Failed fob transponder — the chip inside the fob no longer returns a valid ID.
- Failed LF antenna(s) — around the ignition or inside the vehicle; common on older vehicles.
- Failed RF receiver / RF Hub — the module that listens for the fob's reply.
- Desynchronized key — rolling code drift after a low-battery event or module reset.
- BCM / CAS / FEM fault — the module that authorizes the key has lost its configuration.
Other related symptoms
- "Key Not in Vehicle" warning while the key is clearly present.
- "Push Brake to Start" loop with no start.
- Car cranks but won't fire (classic immobilizer fault).
- Remote start works but push-start fails (LF vs. RF mismatch).
How we diagnose
- Fob test — verify the fob transmits a valid LF response and RF ID.
- Antenna test — check LF field strength at each antenna location.
- Receiver test — confirm the RF Hub / receiver reports fob ID over the bus.
- Module test — check BCM / CAS / FEM for security access faults and stored codes.
- Key re-learn — re-pair keys once the physical fault is corrected.
Makes we diagnose most often for this
Ford (F-150, Explorer, Edge, Fusion), GM (Silverado, Tahoe, Equinox), RAM, Jeep, Chrysler, Nissan, Infiniti, Toyota, Lexus, Honda, Acura, BMW (FEM/BDC vehicles are frequent), Mercedes, Audi and VW.
