A car key that suddenly stops working is rarely one single thing - it can be the battery, the chip, the blade, the car, or the pairing between them. The good news is most causes fall into a handful of common buckets, and you can narrow it down quickly before you call anyone. Here's what to check first, in order of how easy it is to fix.
1. Flat key or car battery
The most common and the easiest. If your remote fob suddenly won't lock or unlock but the physical blade still works the door, the fob's coin battery is the prime suspect - a £2 fix. Likewise, if the car's battery has gone flat or been disconnected, it can forget the key from its memory, so a previously working key suddenly won't start it. A flat car battery also means the central locking may behave oddly. Check both before assuming the key itself has failed.
2. Worn or broken blade
Keys wear. A blade that's been used thousands of times can wear enough to struggle in the lock, and a worn key also wears the lock - a slow spiral. A snapped or bent blade is obvious, but a key that's just stiff or intermittent is often wear you can't quite see. If the blade turns but feels rough, or works sometimes and not others, wear is likely. A locksmith can cut a fresh blade to the original spec rather than copying the worn one.
3. Failed transponder chip
Inside the key is a tiny transponder chip that talks to the car's immobiliser. If that chip fails - through age, damage or a drop - the car opens but the engine won't start, and you'll often see the immobiliser light flash or stay on. This isn't something a new battery fixes; the key needs reprogramming or replacing. A locksmith can test whether the chip is being recognised and code a new one on-site.
4. Lost pairing after a battery change or flat
Sometimes the key and car are both fine, but the car has dropped the key from its memory - common after a flat car battery or a fob battery change on some models. The fix is re-pairing the key to the car, which is a programming job a mobile locksmith can do at the vehicle.
5. Immobiliser or ignition fault
If the engine cranks but won't fire, with a flashing immobiliser light, the fault may be in the immobiliser system itself rather than the key. This sits at the edge of keys and electrics - exactly where an auto locksmith diagnoses. We can tell you whether it's the key or the car, and fix the key side; if it's beyond that, we'll say so honestly.
When to call
If it's a flat fob battery, change it yourself. If the car battery's flat, deal with that. But if the key won't start the car with good batteries, or the immobiliser light is flashing, call a mobile locksmith - we diagnose at the vehicle and fix the key and programming side without a tow. Tell us the make, model and what's happening and we'll narrow it down before we set off.
Need this sorting, not reading about?
Call or WhatsApp East & Co - we come to you across within about 25 miles of Scunthorpe, 24/7.
Quick questions
My remote stopped working after I changed the battery - why?
On some models a fob battery change can drop the key from the car's memory. The fix is re-pairing the fob to the car - a quick programming job at the vehicle.
The engine cranks but won't start - is it the key?
It can be. If the immobiliser isn't recognising the key's chip, the car will crank but won't fire, often with a flashing immobiliser light. A locksmith can diagnose whether it's the key or the car on-site.