A car key can fail in several different ways. The buttons may stop responding, the blade may no longer turn or the vehicle may refuse to start even though the key still fits. Identifying exactly what has failed is the first step towards finding the right solution.
It is never convenient when a key stops working, particularly if you are away from home or in a hurry. However, the problem is not always as serious as it first appears. A flat fob battery, damaged blade or flat vehicle battery can all produce similar symptoms.
Before forcing the key or assuming that it must be replaced, carry out a few straightforward checks.
The main point: identify whether the fault is with the physical key, remote fob, door lock, ignition, immobiliser or vehicle before deciding what to do next.
Why has your car key stopped working?
The symptoms can provide a useful indication of the likely cause:
1. Identify what has actually stopped working
Start by being as specific as possible about the problem. Different symptoms often point towards different causes.
Ask yourself:
- Have the remote buttons stopped responding?
- Will the key no longer unlock the doors?
- Does it open the car but fail to start the engine?
- Is the key blade bent, worn or damaged?
- Has the key stopped turning in the lock or ignition?
- Does the problem affect both the main key and the spare?
- Is there a key or immobiliser warning on the dashboard?
- Are the vehicle’s lights and other electrical systems working?
Make a note of exactly what happens when you use the key. These details will help an auto locksmith distinguish between a mechanical, electrical and programming fault.
2. Try the spare key
If you have a spare key, test it as soon as possible. This is one of the quickest ways to separate a key fault from a vehicle fault.
Test all relevant functions, including the manual door lock, remote buttons and engine start. A spare may work mechanically while still having a separate remote or programming problem.
3. Look for visible damage
Examine the key and fob closely. Even relatively minor damage can prevent a modern key from working correctly.
Common warning signs include:
- A cracked or loose fob casing
- A worn, bent or snapped blade
- Loose, missing or unresponsive buttons
- Signs of water damage or corrosion
- A battery compartment that no longer closes properly
- A blade that moves inside the casing
- Damage around the flip-key hinge
- Exposed internal electronics
A damaged casing can expose the circuit board and transponder to moisture, dirt and physical damage. Do not continue using a visibly damaged key if it feels likely to break inside the lock or ignition.
4. Check the key-fob battery
A flat or weak battery is one of the most common reasons for remote-locking problems.
Possible signs include:
- Reduced operating range
- Intermittent locking or unlocking
- Buttons that only work after several presses
- A keyless-entry system that detects the key inconsistently
- Complete failure of the remote functions
If the manual blade still operates the door but the remote does not, replacing the fob battery may resolve the problem.
How to replace the battery safely
- Check the vehicle handbook for the correct procedure
- Use the correct battery type and orientation
- Open the casing carefully to avoid damaging its clips
- Do not touch or bend internal electrical contacts unnecessarily
- Make sure the casing closes fully after replacement
- Test every remote function afterwards
If the fob stops working after a battery change, it may require resynchronisation, inspection or repair.
5. Check whether the vehicle battery is flat
Sometimes the key is not the problem at all. A flat vehicle battery can prevent the central locking from responding and may leave the car appearing completely unresponsive.
Signs that the vehicle battery may be responsible include:
- No dashboard lights
- No interior lights
- No response from the central locking
- A clicking sound when attempting to start
- Weak or flickering electrical systems
- Both the main key and spare behaving in the same way
If the dashboard, interior lights and other electrical systems are also dead, the vehicle battery is a more likely cause than the key.
Follow the vehicle manufacturer’s guidance or contact a suitable breakdown provider or automotive professional. Do not attempt to jump-start the vehicle unless you understand the correct procedure for that model.
6. Do not force the key
If the blade feels stiff, catches or will not turn, stop rather than applying more pressure.
Forcing the key can:
- Snap the blade inside the lock or ignition
- Damage the ignition barrel
- Damage the door lock
- Bend or weaken the key further
- Turn a small repair into a more expensive one
A worn key or lock may still move slightly before failing completely, so resistance should not be ignored. Avoid applying oil, adhesive or an unsuitable lubricant to the lock.
Stop immediately: if the key is bent, cracked, partially snapped or stuck in the ignition, do not repeatedly twist or pull it. Professional extraction is usually safer than risking a complete break.
7. The key may need reprogramming
Modern car keys often contain a transponder chip that communicates with the immobiliser. If that communication fails, the vehicle may not recognise the key even though the blade still fits.
Possible causes include:
- A faulty transponder chip
- Internal fob damage
- A programming or synchronisation fault
- Water damage
- A damaged circuit board
- Damage caused while replacing the battery
- An incompatible replacement fob
A suitably equipped auto locksmith may be able to test the key, reprogramme it or advise whether replacement is the more practical option.
Key cutting and key programming are different
Read our complete guide to car key programming for more information about transponders, remote fobs and smart keys.
8. The lock or ignition may be faulty
It is easy to assume the key has failed when the underlying problem is actually inside the vehicle.
Possible causes include:
- A worn ignition barrel
- Dirt or debris inside the lock
- A damaged door-lock cylinder
- Internal wear in the locking mechanism
- A central-locking fault
- A steering-lock problem
- An immobiliser or ignition-system fault
If both the main key and spare key have the same problem, the vehicle is more likely to be the source of the fault.
Do not insert tools, spray unsuitable products into the lock or dismantle the ignition. Incorrect treatment can cause additional mechanical or electrical damage.
9. Consider whether signal interference is involved
Keyless-entry and remote systems can occasionally behave differently in particular locations. Electronic interference may prevent the vehicle from detecting the key normally.
If the problem only occurs in one place:
- Move the key closer to the vehicle’s recognised key-detection point
- Remove the key from bags containing other electronic devices
- Keep it away from mobile phones and other keys while testing
- Try the manufacturer’s emergency starting procedure
- Consult the vehicle handbook for the backup key position
Do not repeatedly press the remote buttons while standing a long distance from the vehicle. If the problem continues in different locations, the key or vehicle is more likely to require inspection.
10. Know when to contact an auto locksmith
If the basic checks do not solve the problem, or the key is physically damaged, an auto locksmith can help identify the cause before unnecessary parts are replaced.
Assistance may include:
- Diagnosing a faulty car key
- Testing the remote and transponder
- Vehicle entry after a lockout
- Removing a snapped key
- Repairing or replacing a damaged key
- Supplying and cutting a replacement
- Investigating remote-fob problems
- Programming a transponder or smart key
- Checking whether the lock or ignition is at fault
Not every locksmith supports every vehicle. Provide the complete vehicle details and symptoms before arranging a callout.
What information should you give the locksmith?
Accurate information will help the locksmith understand the likely fault and prepare suitable equipment.
When should you get help urgently?
It is sensible to seek help promptly when:
- You are stranded away from home
- The key has snapped or is about to snap
- The vehicle will not start
- The remote has failed completely
- You are locked out
- The key is stuck in the ignition
- You do not have a spare key
- The lock or ignition is becoming progressively stiffer
- You cannot secure the vehicle
Early attention can prevent further damage and reduce the chance of the fault becoming more difficult or expensive to repair.
If you are currently locked out, read what to do immediately after a car lockout.
Should the key be repaired or replaced?
Whether repair or replacement is appropriate depends on the failed component and the condition of the key.
A proper diagnosis should establish whether the original key can be repaired or whether replacement and programming offer a more reliable long-term solution.
What to remember
A car key can stop working because of a flat battery, physical damage, failed transponder, worn lock, ignition fault, central-locking problem or flat vehicle battery.
Start with simple checks, test the spare key and avoid forcing anything. If the cause is not obvious, professional diagnosis is safer than guessing or replacing parts unnecessarily.
Frequently asked questions
Why does my key unlock the car but not start it?
The physical blade may be correct, but the transponder chip may not be recognised by the vehicle’s immobiliser. Try a working spare and check for a key or immobiliser warning on the dashboard.
Can a flat fob battery stop the engine from starting?
It depends on the vehicle. On many cars, the immobiliser transponder works independently of the remote battery. Some smart and keyless systems use different backup procedures, so check the vehicle handbook.
Why does my spare key work when the main key does not?
This usually points to a fault with the main key, such as a worn blade, weak battery, damaged electronics or failed transponder.
Should I force a stiff key in the ignition?
No. Forcing the key could snap the blade or damage the ignition barrel. Stop using it and arrange an inspection if it does not turn normally.
Why will neither of my car keys work?
If both keys behave in the same way, the problem may be with the vehicle battery, lock, ignition, immobiliser or central-locking system rather than both keys failing simultaneously.
Can an auto locksmith repair a damaged key fob?
Sometimes. A locksmith may be able to replace the battery, casing, blade, buttons or other repairable parts. Severe damage to the circuit board or transponder may require a complete replacement.
Will changing the fob battery erase its programming?
A routine battery change will not normally erase the immobiliser transponder. However, remote functions may occasionally require resynchronisation. Follow the manufacturer’s procedure for the vehicle.
Can a locksmith programme a replacement car key?
In many cases, yes. A suitably equipped auto locksmith may be able to supply, cut and programme a compatible transponder, remote or smart key.
Editorial note: this article provides general information. Diagnostic and repair procedures vary between vehicles. Follow the manufacturer’s instructions and confirm service compatibility, identification requirements and the complete price directly with the locksmith before booking.