Stuck right nowCar keys
Key fob not working in the cold? What to try before you call
A fob that works fine in the kitchen can go silent in a Winnipeg parking lot. Here is why, and how to get in and get started anyway.
Why do key fobs fail at minus thirty?
Your fob runs on a lithium coin cell, usually a CR2032 or similar. Batteries make power through a chemical reaction, and cold slows that reaction down. The battery isn't empty; it just can't deliver its power fast enough to send a strong signal.
The numbers make the point for Winnipeg. Energizer's datasheet rates its CR2032 for an operating range of minus 30 C to 60 C (Energizer CR2032 datasheet). Plenty of January mornings here sit below that. A new battery may cope; one that is two winters old often won't.
That's also why the problem seems to come and go. The fob fails in the parking lot after work, then works fine after ten minutes in your pocket on the bus.
Cold slows the coin battery. Warm the fob in your hand or an inside pocket and try again.
How do I get into the car with a dead fob?
Most fobs hide a metal blade key inside. Look for a small slide or button on the fob's edge; press it and the blade pulls out.
Some cars don't show a keyhole on the driver's door. The cylinder is often hidden under a small cap at the end of the handle, which pops off with the tip of the blade key. Toyota, for example, notes that a mechanical key hidden in the fob will open the driver's door when the battery is dead (Toyota support).
If that lock is frozen too, the steps in frozen car lock: what to do apply. Expect the alarm to sound when you open the door with the blade on some cars; it stops once the car recognizes the fob at the start button.
Slide the hidden blade key out of the fob. The keyhole may sit under a cap at the end of the handle.
How do I start a push-to-start car if the key fob is dead?
The fob contains a passive chip that the car can read at very close range even when the battery is too weak to transmit. So:
- Sit in the driver's seat with your foot firmly on the brake.
- Hold the fob right against the start button, or place it in the backup slot or pad your car uses. Toyota's guidance is to hold the Smart Key next to the START button and press it.
- Press the start button with the fob, or with your finger while the fob touches it.
Where that spot is varies by make: some cars use the button, some a marked area on the steering column, some a slot in the console or cupholder. The owner's manual section on starting the engine when the key battery is dead shows yours. It is worth finding before January rather than in a dark parking lot.
Foot on the brake, then hold the fob right against the start button or in the backup slot your manual shows.
How do I change a key fob battery?
Most fobs open with a coin or a small flat screwdriver at a notch on the seam. Before you buy a battery:
- Read the type printed on the old cell (CR2032, CR2025 and CR1632 look similar but are different thicknesses).
- Note which way up it sits, usually with the printed side facing you.
- Press the fob's buttons a few times after closing it, then test from a few metres away.
Keep a spare battery at home, not in the car. Coin cells are dangerous if swallowed: Energizer warns that swallowing one can cause serious injury or death in as little as two hours, so store spares where small children can't reach them.
Match the type printed on the old cell, and keep spares where small children can't reach them.
My remote starter fob isn't working. Is that the same problem?
Possibly not. An aftermarket remote starter, the kind many Winnipeg drivers add for winter, comes with its own fob and its own receiver under the dash. It has its own battery, often a different size, and it is paired to the starter module rather than to the car's computer.
So if the car's own fob works but the remote start fob doesn't, change the remote starter fob's battery first. If the starter itself has stopped responding, that's a remote starter issue rather than a key issue.
One safety note that matters every winter: never remote-start a car parked in a closed garage. Health Canada advises against idling a vehicle in the garage even with the door open, because carbon monoxide can build up and seep into the house (Health Canada).
It has its own battery, so change that first. Never remote start a car in a closed garage.
When is it not the battery?
A fresh battery should fix a cold-weather fob. If it doesn't, look for these signs:
| What you notice | What it usually means |
|---|---|
| Works only when held against the start button, even when warm | The transmitter or its connections are failing |
| Buttons do nothing, but the car still starts | The remote side has lost its pairing or is damaged |
| Dash says key not detected even with the fob on the button | The chip isn't being read; the fob may need programming or replacing |
| The case is cracked or the fob went through the wash | Moisture damage to the circuit board |
| Your only fob is lost | You need a new one made and programmed to the car |
In those cases the fob needs programming to your car or a replacement. Our technician can program and replace key fobs for most vehicles at your car: see key fob programming and replacement. If every key is gone, read can a locksmith make a car key without the original.
Smart locks at home have the same cold-battery weakness. If your front door keypad has gone dark, see keypad door lock battery dead.
This one is a call, not a fix.
The fob may need programming or replacing, which our technician can do at your car for most vehicles.
Key fob programming and replacementQuestions people ask
- Will a push-to-start car start if the key fob is dead?
- Usually, yes. Most push-to-start cars can still read the fob's chip when it is held right against the start button or placed in a backup slot. Toyota, for example, says to hold the Smart Key next to the START button and press it with your foot on the brake. Your owner's manual shows the spot for your car.
- Why does my key fob stop working in the cold?
- A fob runs on a small lithium coin cell, and batteries deliver less power as they get colder. Energizer rates its CR2032 coin cell for use down to minus 30 C, and Winnipeg mornings regularly go colder than that, so a battery that is already weak can drop out entirely.
- Can a locksmith program a remote starter fob?
- An aftermarket remote starter uses its own separate fob and receiver, so it is paired differently from the car's own key. Tell us the make of the remote starter when you call and we will tell you what it needs.
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