Car Key Fob Stopped Working? Common Causes and What to Check
When a key fob suddenly stops working, the fault could be as small as a coin-cell battery or as involved as a failed remote, damaged board or vehicle-side receiver problem. The symptoms help narrow it down.
Start with the exact symptom
Does the remote fail to lock/unlock but the car still starts? Does the vehicle say the key is not detected? Does one button work but another does not? Did the problem appear immediately after the key was dropped or got wet?
Those differences matter because remote locking, transponder authorisation and proximity detection can be separate functions within the same physical key.
A weak or flat fob battery
A coin-cell battery is one of the simplest causes of weak range or non-responsive remote buttons. Use the correct battery type and polarity for the key. If a fresh quality battery makes no difference, do not keep replacing batteries indefinitely; the fault may be elsewhere.
Some smart keys still contain an emergency blade or have a manufacturer-defined backup start procedure. The vehicle handbook is the correct source for model-specific instructions.
Worn buttons, cracked case or damaged board
Keys live in pockets, bags and work vans, so physical wear is common. Rubber buttons split, solder joints can fail, battery contacts can loosen and cases can crack after a drop.
If the key still starts the vehicle, the transponder or smart-key identity may still be valid even though the remote-button section is damaged. That can make key fob repair worth assessing before full replacement.
When the vehicle says 'key not detected'
A key-not-detected message on a proximity vehicle can be caused by a weak key battery, a failed key, interference, a vehicle battery issue or a vehicle-side detection problem. One symptom does not prove the key itself is faulty.
If you have a second key, testing it is useful: if both keys fail in the same way, the diagnosis may need to look beyond the first fob.
Repair, reprogram or replace?
Repair is appropriate when the fault is physical and the important electronics remain healthy. Reprogramming is relevant when a supported key needs to be learned or authorised to the vehicle. Replacement is needed when the key hardware/electronics are beyond sensible repair or the key is completely lost.
For a lost or unusable key, see car key programming and lost car key replacement.
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Frequently Asked Questions
Will changing the key-fob battery erase the programming?
On many vehicles, simply replacing the coin-cell battery does not erase the immobiliser identity, but model-specific behaviour varies. Follow the vehicle/key instructions.
Why does my key start the car but not unlock it remotely?
The immobiliser/transponder function and remote-locking function can be separate, so one can work while the other fails.
Should I buy a cheap online fob and programme it myself?
Compatibility is more than case shape or button count. Frequency, electronics, transponder type and vehicle generation must match, so an apparently identical fob may not be suitable.
Need Help With a Car Key in Exeter?
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