Key fob not working or key not detected? What to check, in order

How do you start a car if the key fob doesn't work?

Use the metal key hidden inside the fob to open the driver's door. On a push-button car, press the start button with the fob itself, or put the fob in the backup slot your owner's manual shows. RACV says that slot is likely on the dash, the centre console or the steering column.

RACV says the manual key on a modern fob is usually hidden inside it. No keyhole on the door handle? RACV says it's still there, under a cap, usually with a small slot for the tip of the key blade.

Your owner's manual shows the backup spot for your car. Mazda's CX-30 manual, for one, says to press the brake, then line up the badge on the key with the centre of the start button while the button's green light flashes.

Can I still drive my car with a dead key fob?

Once the car has started with the backup method, keep the fob in the car with you. Mazda's manual warns that if the key isn't in the car, the engine won't restart after you switch it off.

Why does my car say 'key not detected' when I have the key?

The car can't pick up the key's signal. Mazda's owner's manual lists a dead key battery, a battery fault or no key in range as the reasons for its 'Key Not Detected' message. Mazda also says its key may not work properly when it's carried with a phone or covered by metal.

1. 1Step 1: Hold the fob against the start button, or use the backup spot in your owner's manual.
2. 2Step 2: Move the key away from your phone. Mazda says its key may not work properly when it's carried with a mobile phone or covered by something metal.
3. 3Step 3: Pick the key up and move it. Toyota says most of its newer smart keys go into a battery-saving mode when they're left still.
4. 4Step 4: Lift the key out of the glovebox or console. Mazda says the engine may not start with the key in a storage compartment.
5. 5Step 5: Try the spare key, then fit a new coin battery.

Can I still drive with no key detected?

If the message comes up while the engine is running, check the key is still in the cabin before you switch off. Mazda shows the same warning when a key that was in the car has been taken out.

Why has my key fob stopped working? What to check first

Check the coin battery first. Mazda's owner's manual says that if the key doesn't respond to a button press, or its working range gets too small, the battery may be weak. After that, look at how the battery is seated, what's sitting near the key, any damage to the fob, and the car itself.

Act fast on a dropped or wet fob. Kia's EV9 manual warns that moisture can make a smart key malfunction, and RACV says a damaged fob should be repaired or replaced urgently, because the battery can come loose. Use the spare and ask about a replacement key or a spare.

What blocks the key fob signal?

Mazda's manual lists a mobile phone carried with the key, a metal object touching or covering it, nearby electronics such as a laptop, and aftermarket electronics fitted to the car.

Key fob not working after a battery change? Check these five things

Open the fob again before you blame the key. Check that the battery faces the right way, that it's the right size, that the metal contacts touch it, whether the cell has a bitter child-safety coating, and that the case is clipped fully shut. Then test the buttons beside the car.

1. 1Step 1: Facing. Mazda's CX-30 key takes its battery positive side up. Yours may differ, so match the marking inside the case.
2. 2Step 2: Size. A CR2025 and a CR2032 are both 20 mm across, but Energizer's datasheets list the CR2025 at 2.5 mm thick and the CR2032 at 3.2 mm. Fit the size printed on the old cell.
3. 3Step 3: Contacts. Mazda warns that bending the metal terminals during a battery change can damage the key. If a tab looks bent or flattened, stop there.
4. 4Step 4: Coating. Apple warns that some CR2032 batteries with a bitter child-safety coating might not work in battery-powered products. Try a cell without it.
5. 5Step 5: Case. Press the two halves together until every clip is home.

A battery change on its own may not call for reprogramming. Mazda's CX-30 steps end when the cover goes back on. RACV says a fob whose battery has been flat for a while may need it.

ABC Locksmiths' walk-in shop handles fob batteries and shells at the Brendale counter.

Why does my key fob start the car when the buttons don't work?

The buttons and the engine start are two separate jobs. The buttons need the coin battery to send their signal. Mazda's manual, for one, says the immobiliser chip in the key talks to the engine controls at short range, and that the engine can still be started with a dead key battery by holding the key to the start button.

So dead buttons on a car that still starts point to the battery or the buttons.

The reverse is a different fault. If the buttons work but the engine won't start, that's a question for transponder key and chip replacement or the dealer. A key that won't turn in the barrel is covered in key won't turn in the ignition.

Does my car key have a chip?

Toyota says engine immobilisers are standard across all its new vehicles, so the engine can't be started without an authorised key. For your car, look under immobiliser or keys in the owner's manual.

How do I reset or resync my key fob to my car?

Start with your owner's manual, because any reset steps belong to one make and model. If the manual lists none, pairing the key is a programming job for a locksmith or a dealer. RACV says a fob whose battery has been flat for a while can generally be cloned from your spare key by either one.

Find your spare key before you book anything. RACV notes that if the spare is lost too, the car's computer system may need to be reset. Mazda's manual says that when its immobiliser system is repaired, every key has to come in to be programmed.

How do you reset a key fob after replacing the battery?

Check the manual first. Mazda's CX-30 battery steps list no reset. If your key stays dead, go back through the five battery checks: facing, size, contacts, coating and case.

Call a locksmith or your dealer with the make, model and year before you spend anything.

Is it the fob or the car? A quick test with your spare

Try the spare key. If the spare works, the fault is in the first fob: its battery, its contacts or the fob itself. If both keys fail, look at the car, or at two batteries of the same age. RACQ says a sluggish start could be a sign the car battery needs replacing, which is a roadside job.

Where can I take a key fob that still won't work?

Take it to an automotive locksmith or your dealer, and bring the spare key if you have one. RACV says a fob can generally be cloned from your spare by either one. Ring first with the make, model and year, because the answer depends on the car. Ask what the job involves before you agree to it.

ABC Locksmiths has a walk-in shop at Unit 19, 193-203 South Pine Road, Brendale QLD 4500. Car key batteries and shells are part of the work there, along with car keys cut and decoded, and spare keys. The shop is an RACQ approved repairer. Shop hours and directions are on the contact page.

Ask before you drive over. Call 07 3205 4925, or send us the make, model and year and pick the remote or fob option.