In short:
- The commonest cause is a flat battery in the fob. Toyota says a smart key battery typically lasts one to two years, however often you use it.
- A weak car battery, strong radio interference or simply being out of range can look like a dead fob.
- Most remotes hide a mechanical key, and many cars can be started with a weak fob by following the handbook's emergency procedure.
- Test with the spare. If the spare works, the problem is in the first fob, not the car.
- If the fob is damaged, lost, or no longer recognised by the car, a car locksmith can test it and quote on site.
What "not working" looks like
Key fob trouble rarely arrives all at once. The pattern of symptoms says a lot about the cause, so notice what's actually happening before you start pressing buttons.
| What you notice | Most likely cause |
|---|---|
| Works only when you're right next to the car | Fob battery running down |
| Warning on the dashboard about the key battery | Fob battery low; many cars warn you before it goes flat |
| Nothing works: no unlock, no interior light, dashboard dark | The car's own 12V battery is flat |
| Fails in one parking area, fine everywhere else | Radio interference at that spot |
| Spare fob works, this one doesn't | The fob itself: battery, damage or lost pairing |
| Buttons work but the car won't start ("key not detected") | Weak fob battery, or the car isn't reading the key's chip |
| Stopped after a drop, a wash or a battery change | Physical damage, a badly seated battery, or the fob needs re-pairing |
Battery: the fob's and the car's
The fob battery is a small coin cell. Toyota UK's help pages put a typical smart key battery life at one to two years, regardless of how often the key is used, and say many models sound a warning and show a message on the display when it's low. The range shrinking over a few weeks is the classic early sign.
The car battery is easy to overlook. If the 12V battery is flat, central locking and smart entry may not respond at all, and no amount of fob batteries will help. A dark dashboard and no interior light when you open the door with the mechanical key point to the car, not the key.
Change a fob battery only the way your vehicle handbook describes. Remote housings vary a lot: some open with a coin, some need the mechanical key pressed into a slot, and some have clips that break if you lever in the wrong place. Use the battery type printed in the handbook or on the old cell, and fit it the right way up.
Signal, range and interference
A remote talks to the car by low-power radio. Toyota lists strong sources of radio waves or electrical noise, such as TV towers, power plants, radio stations, large displays and airports, as things that can interfere. Its smart entry works when the key is within about 0.7 metres of an outside door handle.
In practice, interference tends to show up as a fob that refuses to work in one spot and is fine everywhere else. Try walking right up to the driver's door and pressing again, or move away from any obvious transmitter. Keeping the fob in the same pocket as your phone can also be worth changing if the problem is intermittent.
Toyota also notes that if smart entry hasn't been used for a couple of weeks, some models may only unlock from the driver's door. Your own handbook will say whether your car does anything similar.
Safe checks to try, in this order
- Try the spare fob. If it works, the car is fine and the problem is in the first key.
- Walk right up to the driver's door and try again, away from anything that might interfere.
- Look at the dashboard. A key-battery warning or a "key not detected" message narrows things down.
- Use the mechanical key to open the driver's door. Toyota says most of its smart keys have one, and that the lock is often behind a small cover on the handle. Your handbook shows where it is on your car.
- Use the handbook's emergency start. Many push-button cars let you start with a weak fob by holding it against the start button or placing it in a marked spot. Follow the exact steps for your model.
- Change the fob battery as the handbook describes, then test again.
If none of that helps, stop there. The next steps involve the car's systems, and guessing can make the job longer.
What makes it worse
- Prising the housing open with a knife or screwdriver. Cracked cases and broken clips are a common way a simple battery change turns into a key replacement.
- Drying a wet fob on a heater or in a microwave. Heat damages the circuit board and the battery.
- Ignoring the low-battery warning. If the fob goes flat away from home, you're left relying on the mechanical key and the handbook's emergency start.
- Buying an unbranded replacement shell or remote and hoping it works. Many need to be paired to the car, and not every part is compatible.
- Jump-starting the car without reading the handbook first. Many handbooks set out a specific procedure and connection points.
When to call a car locksmith
It's time for a professional when:
- the fob is damaged, wet through, or cracked open;
- a new battery hasn't fixed it and the spare works fine;
- the car no longer recognises the key, even with a good battery;
- you've lost a remote, or you only have one left and want to sort it out before it fails;
- you're locked out and the mechanical key won't open the door.
Car keys are one of our everyday services; our car locksmith service page explains them. We're open 24/7, and the technician comes to wherever the car is: home, office car park or shopping centre. The R250 call-out fee. The technician assesses the job on site and gives you the price before any work starts. Nothing is done until you agree. Payment is by EFT, cash or card. The technician asks for proof that the car is yours before doing any work on its keys or locks. We don't do key cutting or key duplication.
What to send us before we arrive
- Make, model and year, and whether it has push-button start.
- Photos of the fob, front and back, and of any dashboard warning.
- Whether the spare works, and whether you've already changed the battery.
- Where the car is and how to get to it: the estate gate, office park security or parking level.
- Proof of ownership you can show: ID with the registration papers or licence disc details.
If a child or pet is ever locked inside, read child or pet locked in a car: what to do first before anything else. For the rest of what we do, visit our mobile locksmith in Centurion homepage.
Questions
I changed the battery and now the fob doesn't work at all. What happened?
Check that the new cell is the right type and the right way up, and that the housing has clipped shut properly. Some cars also need the remote re-paired after a battery change; your handbook will say. If it still doesn't respond, a car locksmith can test it.
Can you copy my car key?
No, we don't do key cutting or key duplication. We can look at the key and the car on site, explain what's wrong and what the options are, and quote before any work.
Why does my remote work at home but not at one office park?
That pattern usually points to radio interference at that location, not a faulty key. Try again right next to the driver's door. If it keeps happening in more places, have the fob battery checked.
Need a locksmith to look at it?
If this hasn't solved the problem, our car keys & lockouts service covers it. We're a mobile locksmith in Centurion, so we come to your door.
Sources and further reading
- Toyota UK: What to do if your Toyota won't unlock — Depleted key battery as a common cause; flat 12V battery stops smart entry; radio interference; about 0.7 m range; driver's-door-only unlocking after a long period unused; the hidden mechanical key; refer to the owner's manual.
- Toyota UK: Help centre — Smart key batteries typically last one to two years; low-battery alert and display message; sources of interference such as TV towers, power plants, radio stations and airports.