Why Is My Car Key Not Working?
A car key stops working because of a flat key fob battery, a fault in the remote electronics, a worn blade, a transponder chip the immobiliser does not accept, a fault in the lock or a flat car battery.
Inta-Lock Car Key Guides. Updated October 2026.
The symptom shows where the fault sits. Remote buttons that do nothing point to the key fob battery or the remote electronics, a blade that does not turn points to the blade or the lock, and a key that turns with no start points to the immobiliser or the battery of the car.
The spare key is the first test. This guide sorts six symptoms in one table, gives the short answer for each and names the page that owns the detail.
Why Does a Car Key Stop Working?
A car key stops working because one of six parts has failed, the key fob battery, the remote electronics, the blade, the transponder chip, the lock or the battery of the car.
- Key fob battery. The key fob battery is the coin cell that powers the remote buttons. A low cell shortens the range first and then stops the buttons.
- Remote electronics. The remote electronics are the circuit board and the contacts inside the key. Water, a drop or worn buttons stop the signal while the battery is still good.
- Blade. The blade is the cut metal part that turns a lock. A worn, bent or cracked blade no longer fits the lock it was cut for.
- Transponder chip and immobiliser. The transponder chip is the part of the key that the immobiliser reads before the engine starts. A chip that is damaged or not stored in the car leaves the engine stopped.
- Lock. The lock is the door lock or the ignition lock that the blade turns. Wear or dirt inside a lock stops a sound key from turning.
- Battery of the car. The battery of the car powers the central locking and the immobiliser. A discharged battery stops a working key from operating the car.
The symptom shows which of the six parts of the key and the car has failed.
Which Symptom Points to Which Part of the Key?
Six symptoms sort a car key that has stopped working by where the fault sits, each with a first check at the car.
| What the key does | Where the fault sits | First check at the car | Where the detail is |
|---|---|---|---|
| The remote buttons do nothing and the blade still works | The key fob battery or the remote electronics | Try the spare key, then fit a new cell of the type the handbook names | Remote buttons section, and key fob repair |
| The blade does not turn the door lock | The blade or the door lock | Try the blade in another lock of the car, then the spare key | The guide to a key that does not unlock the door |
| The key turns and the engine does not start | The transponder chip, the immobiliser or the battery of the car | Watch the immobiliser light with the ignition on, then try the spare key | Engine section, and immobiliser diagnostics |
| The keyless car does not detect the key | The key fob battery, the keyless electronics or the battery of the car | Use the backup start the handbook shows for a low key battery | Keyless section, and the keyless entry guide |
| One key fails and the other key works | The key that fails, not the car | Compare the two keys on the same lock and the same start | Two keys section |
| Nothing works after a battery change | The new cell, the pairing of the remote, or the battery of the car | Check the type and the direction of the cell against the handbook | Battery change section |
A key that shows two symptoms points to the part the two rows share.
What Do You Check First When a Car Key Stops Working?
Five checks at the car, in order, place the fault in the key, in the lock or in the car before anyone is called.
- Try the spare key. A spare that works places the fault in the first key, and two keys that both fail point to the car.
- Look at the interior lights. Lights that stay dark or dim point to the battery of the car and not to the key.
- Press a remote button close to the car. A remote that works only at short range has a low key fob battery.
- Use the blade in the driver door. On a keyless key the blade is stored inside the fob, and the handbook of the car shows how it is released.
- Read the dashboard with the ignition on. An immobiliser light that keeps flashing means the car has not accepted the key.
None of the five checks involves force, because force is what snaps a key blade in a lock.
A car key that has stopped working in Leicester or Leicestershire? Call Matt with the registration and the symptom, and a quote is agreed before work begins.
Call Matt on 0116 442 2084Why Do the Remote Buttons Do Nothing?
The remote buttons do nothing when the key fob battery is low, the remote electronics have failed, the remote has lost its pairing with the car, or radio interference blocks the signal.
One manufacturer handbook lists the causes of a remote that does not operate the central locking as a fault in the remote, the range being exceeded, a battery voltage that is too low, repeated presses out of range that leave the remote to be synchronised again, and interference from stronger radio waves.
Interference belongs to a place, so a key that fails in one car park and works at home is not faulty. One manufacturer guide names television towers, power plants, radio stations, large displays and airports as sources.
A remote with a new battery that still does nothing has a fault in the remote electronics or in its pairing. A bladed key with a dead remote still starts the engine, because the car powers the chip at the ignition lock.
Why Does a Car Key Not Work After a Battery Change?
A car key does not work after a battery change because the new cell is the wrong type or sits the wrong way round, or because the remote is no longer synchronised with the car.
A battery change means two different things. After a new key fob battery, the handbook of the car names the cell type and shows which face sits upward. One manufacturer handbook tells the owner to hold the cell by its edges and not to touch the circuit board.
After a new battery in the car, the remote and the car are sometimes no longer synchronised. The handbook of the car states whether the owner synchronises the remote again and how. Where it gives no owner procedure, the remote is paired again through key programming. A change of key fob battery does not normally remove the programming of the key.
A key fob holds a button battery. The Office for Product Safety and Standards, in its button battery safety campaign, tells households to store spare cells out of the reach of children, because a dead button battery still holds enough power to badly hurt a small child.
Why Does the Blade Not Turn the Door Lock?
The blade does not turn the door lock because the blade is worn, bent or cracked, or because the door lock itself is worn, dirty or seized.
The same blade tried in another lock of the car separates the two. A blade that turns the ignition and not the door points to the door lock, and a blade that fails in each lock points to the blade.
The causes on the blade side and the causes on the lock side are set out in the guide to a car key that does not unlock the door.
Why Does the Key Turn and the Engine Not Start?
The key turns and the engine does not start when the immobiliser has not accepted the transponder chip of the key, or when the battery of the car is too low to turn the engine.
The two causes look different. A low battery of the car gives dim lights and a slow or silent starter. An immobiliser that has not accepted the key leaves the lights bright while the engine does not run.
One manufacturer handbook states that an immobiliser indicator that flashes with the ignition on means a fault in the system and that the engine cannot be started. Its instruction is to switch the ignition off, try again, then try the spare key.
A spare key that starts the engine places the fault in the chip of the first key. How the car checks a key at each start is explained in the guide to the car immobiliser.
Why Does a Keyless Car Not Detect the Key?
A keyless car does not detect the key when the key fob battery is low, the battery of the car is discharged, interference blocks the signal or the keyless electronics have a fault.
One manufacturer handbook lists four conditions in which its keyless key does not work properly, a low key battery, locking and unlocking used continuously, a door handle pulled while the key is operated, and a discharged battery of the vehicle.
Makers build in a backup for a low key fob battery. The blade stored inside the fob unlocks the driver door, and the handbook of the car shows where to hold the key so that the car reads it. On one model the start switch is touched with the key itself.
A keyless key that stays undetected with a new battery, while the spare key is detected, has a fault in its own electronics. How the system works belongs to the guide to keyless entry systems.
What Does It Mean When Only One of Two Keys Fails?
One key that fails while the other key works means the fault sits in the failed key and not in the car.
The working key clears the battery of the car, the locks, the receiver and the immobiliser together. It leaves four parts of the failed key to check, the key fob battery, the remote electronics, the blade and the chip.
A car with one working key left has no such test. For a second hand vehicle bought with only one working key, the car security guidance of Thatcham Research is to have the missing keys deleted and a spare added as soon as possible.
When Is an Auto Locksmith Called for a Car Key Fault?
An auto locksmith is called when the spare key and a new key fob battery have not restored the key, when no spare exists, or when the car accepts neither key.
Whether the fault is one for a repair to the key, a new key or diagnostics on the car is confirmed on the call.
Identity and authority to request the work are checked before key work. The V5C vehicle registration certificate, which names the registered keeper, and photo identification are common examples, and what applies is confirmed on the call.
Where Does a Failed Car Key Lead Next?
Four questions sit beyond a key fault found on this page.
How Does a Key Fob Repair Differ From a New Key?
A key fob repair keeps the key the car already accepts and restores the part that failed, while a new key is cut and programmed to the car from the start.
Worn buttons, a cracked case and a damaged circuit board are faults of the remote electronics, and that work belongs to key fob repair in Leicester. Whether one fob is repaired or replaced is confirmed on the call.
Which Faults Call for Immobiliser Diagnostics?
A car that accepts neither key places the fault in the car and not in the key.
Finding which part of the system has failed is the work of immobiliser diagnostics on the factory system of the car.
What If the Key Does Not Turn in the Ignition?
A key that goes into the ignition lock and does not turn is a mechanical fault, not an electronic one. The causes and the release of a locked steering wheel are set out in the guide to a car key that does not turn in the ignition.
What Happens When the Key Is Beyond Repair?
A key with a snapped blade, a failed chip or water damage across the circuit board is usually replaced and not repaired. What to know before a new key is made is set out in the car key replacement guide.
What the fault in your car key involves is confirmed on the call.
Frequently Asked Questions
Why has my car key suddenly stopped working?
A car key suddenly stops working when the key fob battery runs flat, the remote electronics fail, the blade or the lock wears out, the immobiliser does not accept the chip, or the battery of the car is discharged.
The spare key is the first test, and a spare that works places the fault in the first key.
Does changing the key fob battery remove the programming?
No, a change of key fob battery does not normally remove the programming of the key.
Where the remote stops answering after the change, the handbook of the car states whether the owner synchronises the remote again.
Does a car start with a flat key fob battery?
A car with a bladed transponder key starts with a flat key fob battery, and a keyless car starts through the backup the maker provides.
For a keyless key, the handbook of the car shows where the key is held for the car to read it.
Why does my key unlock the car and not start the engine?
A key that unlocks the car and does not start the engine has a working remote and a transponder chip that the immobiliser has not accepted, or the battery of the car is too low to turn the engine.
The remote and the chip are separate parts of one key.
How much does it cost to fix a car key that has stopped working?
The cost of fixing a car key that has stopped working is set by where the fault sits, in the battery, the remote, the blade, the chip or the car.
No price list is published, and a quote is agreed before work begins.