Car Key Fob Not Working? What to Check Before You Replace It

Your key fob worked yesterday, and today the doors ignore it. Before you assume it is broken, run through a few checks. Many fob problems come down to something simple, and knowing which one you have tells you whether it needs a battery, a spare or a replacement.

Check 1: The battery

A weak battery is the most likely cause, and it rarely fails all at once. The warning signs build up over days or weeks:

• You have to stand closer to the car than before.
• The buttons need two or three presses.
• The dashboard shows a message that the key is not detected or its battery is low.
• Only some buttons still work.

The battery is usually a flat coin cell, and its type is printed on the battery itself. The owner's manual shows how to open the case, which often comes apart with a small slot or a coin. Note which way the old battery faces before you take it out.

Check 2: Is it the fob or the car?

Try the spare fob. If the spare works, the problem is in your everyday fob. If neither one works, the problem is more likely on the car's side, and a weak car battery is a common culprit: the locks and the key sensor both need power.

Check 3: Look for physical damage

Fobs live hard lives in pockets and bags. Check for a cracked case, a button that feels loose or stuck, a broken key ring loop, or signs that it got wet. A fob that went through the washing machine may come back to life after drying out completely with the battery removed, but do not count on it.

Check 4: Rule out interference

Radio signals can drown out a fob. If it fails only in one place, such as near a large building, a radio tower or a row of other cars, try again a few steps away. If it works everywhere else, the fob is fine.

How to open and start the car with a dead fob

Almost every fob or smart key hides a small metal key inside the case. Slide or press the release, pull it out, and use it in the driver's door lock, which is sometimes behind a small cover on the handle.

Starting the car is also possible on most push-button cars. There is a backup spot where the car can read a fob with a dead battery: often you hold the fob against the start button, or place it in a marked spot on the steering column or in the console. The owner's manual shows exactly where.

Signs the fob really needs replacing

• The buttons do nothing even with a fresh battery.
• The car no longer recognizes the key at all.
• The case is broken and the insides are damaged.
• The fob is lost, or you are down to your last working one.

Replacing a fob means cutting the hidden key and programming the new fob to the car, which can be done where the car is parked. If you are not sure which type of key your car uses, our guide to transponder keys, fobs and smart keys will help.

Keep it working longer

• Change the battery at the first warning, not after it dies.
• Keep the fob away from water, and out of the pocket that goes through the wash.
• Use a separate ring so heavy keys do not strain the fob's loop.
• Keep a working spare at home. It turns a dead fob into an inconvenience instead of a lockout.