Is the fob dead, or is it just the battery?

A dead key fob is one of the few automotive problems where the fix is often a two-dollar part and five minutes in a car park. It is worth ruling that out before booking anything, because the alternative — cutting and pairing a replacement — is a real job with a real price.

Check 1: does the spare work?

If you have a second fob, this is the fastest diagnostic you own. A working spare means the car is fine and the fault is inside the first fob. Both dead at once points somewhere else — the vehicle's own battery, or the receiver — because two fobs rarely fail the same week.

Check 2: hold it against the start button or the handle

Nearly every push-to-start vehicle has a backup reader, usually behind the start button itself or in a marked spot on the steering column, and many bladeless door handles read the key at very close range. If holding the fob against it makes the car respond, the passive transponder is alive and well and only the battery-powered remote half has stopped. That is a coin cell, essentially every time.

Check 3: change the battery properly

Open the fob at the seam with a coin or a small flat screwdriver. Before lifting the old cell out, note which face is up — fitting it inverted is the most common reason a fresh battery appears not to help. Fit the same type, usually a CR2032 or CR2025, avoid touching the board, and close it until the seam is fully seated. Then test from a few metres away rather than with the fob against the glass.

On the great majority of vehicles this does not erase anything. The pairing is stored in the car, not in the battery.

Check 4: distance and interference

If range shortened rather than vanished, try somewhere else before concluding the fob is faulty. Underground parking, loading docks and spots near transmitters can drown out a fob's signal entirely, and a fob that works on the street and not in the garage is describing the garage.

What each outcome means

• Spare works, new battery fixes it. Done. No locksmith required.
• Car responds to the backup reader but the buttons never work. The remote circuit has failed — replacement and pairing.
• Nothing responds at all, on either fob. Look at the vehicle before the keys: a flat car battery presents exactly like this.
• The engine will not start although the doors work. That is a transponder or immobiliser issue, not a remote one — see how transponder keys work.

When it really is the fob

Fobs die in three ordinary ways: water, a cracked board from repeated drops, and worn button contacts. A replacement has to be paired to the vehicle, which is the same operation as programming a proximity key. If your car currently has one working fob and one dead one, that is the moment to fix it — a single-key vehicle is the setup that turns a lost key into an all-keys-lost job.