Key fob not working in the cold and damp? What to try first

Why does a fob quit on a cold, damp morning?

Most fobs run on a small lithium coin cell, often a CR2032. A battery makes power through a chemical reaction, and cold slows that reaction. The cell isn't empty, it just can't push out enough current to send a strong signal.

A healthy battery copes fine with a Nova Scotia winter. Energizer rates its CR2032 to keep working well below freezing (Energizer CR2032 datasheet). The trouble is a cell that is two or three years old. It has little to spare, so the first chilly morning with the car parked outside is when it gives up.

That is why the fault comes and goes. The fob fails in the driveway at seven, then works after twenty minutes in your coat pocket.

How do I unlock the door when the fob is dead?

Nearly every fob hides a metal blade key. Look for a small release button or slide on the edge, press it, and pull the blade out.

On many newer cars the driver's door doesn't show a keyhole. It is usually under a small cover at the end of the door handle, which you lever off with the tip of the blade. Toyota, for one, says the mechanical key inside the fob opens the driver's door when the fob battery is dead (Toyota support).

After freezing rain, the lock itself can be iced shut. Frozen car lock: what to do covers that. Some cars sound the alarm when you open the door with the blade; it stops once the car reads the fob at the start button.

How do I start a push-button car with a dead fob?

Inside the fob is a passive chip the car can read at very short range, even with a flat battery. Here is the usual routine:

1. Get in and press the brake pedal firmly.
2. Hold the fob against the start button, or put it in the backup slot or marked pad your car uses. Toyota's instructions are to hold the Smart Key next to the START button.
3. Press the start button, with the fob or with your finger while the fob touches it.

The spot varies by make: the button itself, a marked area on the steering column, or a slot in the console or cupholder. Look it up in the owner's manual under starting the engine with a dead key battery, ideally in your driveway on a dry day, not in a dark parking lot in sleet.

Could salt and damp be the problem?

If the fob works some days and not others, even with a newer battery, look inside it. Salt air, wet mitts and slush on your hands all get into the seam of a fob over a winter. Moisture plus salt corrodes the small metal tabs that hold the battery, and a corroded tab makes a poor connection, worst of all when the battery is cold.

Open the fob and look for green, white or brown crust on the contacts or the battery itself.

• Let the fob dry out fully at room temperature, case open.
• Clean light crust off the contacts with a dry cotton swab or a pencil eraser.
• Put in a fresh battery, close the case firmly, and test it.

If the circuit board itself looks corroded, or the fob went through the wash or into a puddle, cleaning may not be enough.

How do I swap the fob battery?

Most fobs split open with a coin or a small flat screwdriver at a notch along the seam. Before you buy a battery:

• Read the number on the old cell. CR2032, CR2025 and CR1632 look alike but are different sizes.
• Note which side faces up, usually the printed side.
• Once it's closed, press each button a few times and test from a few metres away.

Keep a spare at home rather than in the glovebox. Coin cells are dangerous if swallowed: Energizer warns that a swallowed coin cell can cause serious injury or death in as little as two hours, so store spares well out of children's reach.

What if the remote starter fob is the one that quit?

That is often a separate problem. A remote starter added after you bought the car has its own fob, its own battery and its own receiver under the dash, paired to the starter rather than to the car's computer.

So if the car's own key works but the remote start fob doesn't, change the remote starter fob's battery first. If the starter itself stops responding, the issue is with the starter, not the key.

Whatever the fob, 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 get into the house (Health Canada). That matters during a storm outage too, when it can be tempting to warm up the car inside.

When a new battery doesn't fix it

A fresh battery and clean contacts should cure a weather-related fob. If they don't, the table below points to the likely cause.

Any of these means programming or a new fob. For most vehicles our technician can do both 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.

Keypads and smart locks at home share the same cold-battery weakness. If your front door keypad has gone dark, see keypad door lock battery dead.