Yes, a dead battery in a key fob causes a car not to start when the car has keyless entry and a start button, because the car no longer detects the key. A car with a key that turns in the ignition is the exception and still starts, because the transponder chip in the key takes no power from the 3 volt fob battery. A keyless car with a dead key fob battery still starts with the fob held against the start button.
Dead Key Fob Start Finder
Pick the make of the car.
Hold the fob against the start button. Press the brake pedal, then press start.
Hold the fob against the start button, or use the key slot on older models. Press the brake pedal, then press start.
Press the start button with the fob, with the brake pedal pressed.
Hold the fob against the mark on the steering column. Press the brake pedal, then press start.
Hold the fob against the mark on the steering column. Press the brake pedal, then press start.
Place the fob in the backup slot in the centre console or on the steering column. Press the brake pedal, then press start.
Place the fob in the pocket in the centre console. Press the brake pedal, then press start.
Put the key card in the card reader slot, then press start.
Place the key on the marked spot in the centre console. Press the brake pedal, then press start.
No luck at the backup position? Call 07830249408 and I talk you through it by phone.
Stuck right now? Call 07830249408 in Devon, Dorset or Somerset. I talk you through the backup start by phone before any call out.
The sections below explain why a dead key fob battery stops the start, the 4 signs of a low battery, the 4 steps that start the car anyway and the backup position for 9 make groups. The later sections separate a fob battery fault from a car battery fault and cover the point where a new battery is not enough and key fob repair and replacement takes over.
Hold the dead key fob against the start button, press the brake pedal and press start. Open the door first with the emergency key blade inside the fob. Fit a new CR2032 battery before the engine is switched off again.
Why Does a Dead Key Fob Battery Stop a Car Starting?
A dead key fob battery stops a car starting because a keyless car looks for a radio signal from the fob before the start button works. The car sends a search signal at about 125 kHz, and the fob answers on 433 MHz with power from its battery. A dead battery sends no answer, so the immobiliser stays active and the engine does not start. The dashboard shows a key not detected message or a key fob battery low message.
A key fob is a small radio remote with a 3 volt coin cell, an antenna and a passive transponder chip. The key fob locks, unlocks and identifies the key to the car. The chip of the key fob takes no power from the battery, and the car reads the chip at a range of a few millimetres, which is why the backup start works with a dead battery. A car with a key that turns loses only the remote locking.
What Are the Signs of a Low Key Fob Battery?
The 4 signs of a low key fob battery are listed below, and each sign appears before the fob stops starting the car.
- The remote locking range shortens, so the car responds only from close by.
- The buttons work on the second or third press.
- The dashboard shows a key fob battery low warning, or a flashing red car with key icon on a Nissan.
- The car unlocks more slowly on approach, on keyless entry systems.
Replace the key fob battery in the same week as the first sign. A CR2032 coin cell costs under £3, and a spare cell kept in the glovebox is ready for the day the fob stops.
How Do You Start a Car With a Dead Key Fob in 4 Steps?
Start a car with a dead key fob in 4 steps, which are opening the door with the emergency key blade, holding the fob against the start button, finding the backup position for the fob and replacing the key fob battery. The 4 steps work because the car reads the passive chip in the fob at close range.
Open the Door With the Emergency Key Blade
Open the door with the emergency key blade inside the key fob. Press the release catch on the fob and pull out the metal blade. The lock sits under a small cover on the driver door handle. Open the door, then start the car with step 2.
Hold the Fob Against the Start Button
Hold the fob against the start button with the brake pedal pressed, or the clutch pedal on a manual car, and press start. The reader behind the button picks up the passive chip at a range of a few millimetres. The method works on most Toyota, Nissan, Kia and Hyundai models.
Find the Backup Position for the Fob
Find the backup position for the fob in the table below. Some makes read a dead key fob at a marked position or in a slot, and not at the start button.
Replace the Key Fob Battery
Replace the key fob battery with a new coin cell, after opening the fob with a small flat screwdriver or a coin. Most fobs take a CR2032, and some take a CR2025 or a CR2016, so read the number on the old battery. A branded cell lasts longer than an unbranded cell.
The table below lists the backup position for a dead key fob on 9 make groups.
| Make | Backup Position on Many Models |
|---|---|
| Toyota, Lexus | Hold the fob against the start button |
| Nissan | Hold the fob against the start button, or use the key slot on older models |
| Kia, Hyundai | Press the start button with the fob |
| Volkswagen, Audi, Seat, Skoda | Hold the fob against the mark on the steering column |
| BMW, Mini | Hold the fob against the mark on the steering column |
| Ford | Place the fob in the backup slot in the centre console or on the steering column |
| Vauxhall | Place the fob in the pocket in the centre console |
| Renault | Put the key card in the card reader slot |
| Mercedes | Place the key on the marked spot in the centre console |
The backup position differs between models and years. The vehicle handbook lists the exact place under emergency start or key battery low.
Is the Fault the Key Fob Battery or the Car Battery?
The dashboard separates a dead key fob battery from a flat car battery. The table below compares the 2 faults on 5 signs.
| Sign | Dead Key Fob Battery | Flat Car Battery |
|---|---|---|
| Dashboard lights | Bright as normal | Dim, flickering or off |
| Dashboard message | Key not detected or key battery low | No message in most cases |
| Remote locking | Fails with this fob, works with the spare fob | Fails with every fob |
| Starter motor | Silent | Clicks or turns slowly |
| Backup start position | Starts the car | Changes nothing |
A flat car battery stops every key fob from working, because the receiver in the car has no power. A car battery below about 11.5 volts also makes the keyless system erratic, so charge or jump start the car before blaming the key fob. A flat car battery is the most common reason a car does not start, and it also leaves a key not turning on cars with an electronic steering lock.
Why Does a Car Not Start After a New Fob Battery?
The 4 reasons a car does not start after a new fob battery are lost pairing, a damaged fob, a flat car battery and a fob beyond repair. Key fob repair and replacement covers the second reason, and car key programming covers the first.
Lost Pairing
Lost pairing means the key fob has a good battery and is no longer recognised by the car. Removing the battery triggers the fault on some older fob designs. The fob is programmed to the car again with diagnostic equipment.
Damaged Fob
A damaged fob has water inside, a cracked circuit board or worn battery contacts, and stays dead with a new battery. A fob that has been dropped or washed is the usual case. A repair restores the contacts and the board, or a replacement fob takes over.
Flat Car Battery
A flat car battery leaves the receiver without power, so the car recognises no key fob. Charge or jump start the car before testing the fob again.
Fob Beyond Repair
A key fob beyond repair is replaced with a new fob cut and programmed to the car. A mobile auto locksmith supplies and programs the fob at the car, with no dealer visit.
How Much Does a Dead Key Fob Cost to Fix?
A dead key fob that stops a car starting costs from under £3 to £400 or more to fix, by fault. The table below lists the 5 fixes with typical UK prices.
| Fix | Typical Cost |
|---|---|
| New CR2032 battery, fitted by the driver | Under £3 |
| Key fob programming, fob works and pairing lost | £60 to £120 |
| Key fob repair, circuit board or contacts | £40 to £80 |
| New key fob supplied and programmed by a mobile auto locksmith | £120 to £250 |
| New key fob through a main dealer | £200 to £400 or more |
The fault behind a dead key fob is confirmed by phone before any charge, from the make and the symptoms. Spare car keys are cut and programmed at the car on the same day.
Does Breakdown Cover Help With a Dead Key Fob?
Breakdown cover helps with a dead key fob and a car that does not start on some policies. A breakdown patrol often handles a basic key fob fault as part of a call out. Programming and replacement keys usually require a specialist. Check the policy wording for keys cover or lockout cover before calling.
Frequently Asked Questions About a Dead Key Fob Battery
No, a key fob does not lock, unlock or start a car with a dead car battery, because the receiver in the car has no power. The emergency key blade still opens the driver door.
The engine keeps running if the key fob battery dies while driving, and the dashboard shows a key not detected warning. The car does not restart after the engine is switched off until the fob is held at the backup position.
No, a low key fob battery does not drain the car battery. The key fob and the car run on separate batteries.
No, a car with an ignition barrel and a key that turns still starts with a dead key fob battery. The transponder chip in the key blade has no battery and takes power by induction from the ignition barrel. A dead fob battery stops the start only on cars with a start button.
Key fob buttons work when the car does not start because the lock buttons run at close range on a battery that is too weak for keyless starting. Hold the fob against the start button, and replace the battery straight away if the car starts. A Nissan reports the same fault as a flashing red car with key icon, which goes out once the car reads the fob at the start button.
Key fob batteries last 2 to 4 years on a button remote and 1 to 3 years on a keyless fob, which answers the car throughout the day. Replace the battery when the locking range starts to shorten.
Yes, you can drive to a shop for a battery once the car starts, because a running engine does not rely on the key fob and the car does not cut out on the way. Fit the new battery before switching the engine off again.
No, reprogramming a key fob after replacing the battery is not required on most modern vehicles, because the programming is stored in the chip and does not rely on the battery. A small number of older models require a reset routine from the handbook. A fob that has lost pairing is paired again by car key programming at the car.
A key fob that got wet works once it dries out in some cases. Remove the battery at once, dry every part and wait 24 to 48 hours before testing. A key fob that still fails has corrosion on the circuit board or the battery contacts.
Yes. A mobile auto locksmith supplies and programs a replacement key fob for most makes at the car, usually faster and cheaper than a main dealer. The same visit covers spare car keys, cut and programmed before the only fob fails.
Yes, a dead car battery stops the key turning on cars with an electronic steering lock, because the lock has no power to release the steering column. A key not turning has 6 causes, and a flat car battery is 1 of the 6.
Dean answers in plain words
Does a dead key fob battery really stop the car?
Yes, on a push button car it does. It is one of the most common call outs I get, and 9 times out of 10 it is sorted in under 5 minutes once you know where to hold the fob.
Which battery do you buy?
A branded CR2032 for most fobs. The quality difference is real, and a good one lasts a lot longer.
What if a new battery does nothing?
Then it is the pairing, the fob itself or the car battery. Call me and I give you an honest answer and a price before I come out.
Based in Honiton. Working since 2009. Key fob programming equipment for most common makes.
Honest assessment and a price before I travel. Available 24 hours a day.