A car key fob that has stopped working is annoying, but it rarely means buying a whole new key. Most faults come down to a flat battery, worn buttons, a cracked case or water damage - all of which can usually be put right for £40-£80 with no reprogramming, because the transponder chip inside is untouched. Knowing which fault you have saves you from paying replacement prices for a repair job.
Is it the fob, or is it the car?
The first thing to work out is whether the fault is in the key or in the vehicle. A quick way to narrow it down:
- The car still starts, but the remote locking is dead - almost always the fob: a flat battery, worn buttons or a tired remote board.
- The remote works but the car won't start or recognise the key - more likely the transponder side, the immobiliser, or a failing start button.
- Nothing works at all - start with the battery (cheap to rule out), then look at the fob electronics.
If you have a spare key, try it. If the spare behaves perfectly, the problem is in the first fob, not the car.
The common fob faults - and the fix
Flat battery
By far the most common cause. Most fobs use a CR2032 or CR2025 coin cell that lasts two to four years. Symptoms are a shorter remote range first, then no response at all. This is a few pounds in parts and a five-minute job - see the steps below.
Worn or unresponsive buttons
Years of pressing wear out the rubber pad and the contacts beneath it. One button stops working, then another. The board can often be cleaned or the button pad replaced; if the contacts are gone, a replacement remote board restores full function.
Cracked or broken case
A dropped key or a worn keyring loop can crack the shell so the buttons fall out or the blade goes loose. The chip and board are usually fine - they just need transferring into a new case (see below).
Water damage
A fob through the wash or dropped in a puddle can corrode the board. Caught quickly, it can sometimes be cleaned and dried; if the corrosion has spread, the remote board is replaced and the chip reused.
Dead remote, working chip
Sometimes the remote electronics fail while the immobiliser chip still works - so the car starts but won't lock remotely. A remote repair or board swap fixes this without touching the programming.
How to replace a car key fob battery
If you want to rule out the cheapest cause yourself first:
- Find the right battery. Usually a CR2032 or CR2025 - the size is printed on the old cell once the fob is open.
- Open the fob. Slide out the emergency blade and use the slot it leaves, or gently prise the seam with a small flat tool. The case clips together - don't force it.
- Swap the battery. Note which way up the old cell sits and fit the new one the same way, keeping fingers off the flat faces.
- Close and test. Clip the case shut, refit the blade and test lock, unlock and boot. If the remote still fails, the fault isn't the battery.
Repair or replace? The honest answer
A repair keeps your existing programmed key and only touches the broken part, so it is always cheaper. Replacement - a new fob that has to be cut and programmed to the car - is only the right call when the electronics have genuinely failed or the chip is lost. A straight-talking locksmith will tell you which camp your key is in before quoting.
| Job | Typical price | Reprogramming? |
|---|---|---|
| Battery replacement | £3-£15 (DIY) / £15-£30 fitted | No |
| New case, chip transferred | £40-£80 | No |
| Remote board repair / replacement | £60-£120 | Sometimes |
| Full fob replacement (cut & programmed) | £100-£250 | Yes |
| Proximity smart-key repair | £80-£180 | Sometimes |
Need a full replacement rather than a repair? See car key replacement in London for the mobile, same-day options.
Frequently asked questions
Can a car key fob be repaired instead of replaced?
Very often, yes. A flat battery, worn buttons, a cracked case or a snapped blade can usually be fixed for £40-£80 with no reprogramming, because the transponder chip is untouched.
Replacement is only needed when the fob has failed electronically or the chip is lost.
My fob stopped working after a battery change - why?
Usually the new battery is the wrong size, fitted upside down, or making weak contact. Occasionally the buttons or board are worn and the battery was only part of the problem.
If a known-good, correctly fitted battery doesn't restore it, the fob itself needs attention.
Can the chip be moved into a new fob case?
Yes. If the casing is cracked or the buttons are worn but the electronics still work, the chip and remote board can be transferred into a fresh shell. The car still recognises the original chip, so there's no reprogramming and the cost stays low.
How much does car key fob repair cost?
A battery change is a few pounds in parts. A new case with the chip transferred is typically £40-£80, and a full remote repair £60-£120.
Only if the fob has to be replaced and reprogrammed does the price rise to £100-£250 depending on the car.
Need a fob repaired or replaced in London?
Bullard Locks is a mobile auto locksmith covering North and Central London. Fob batteries, cases, buttons and remote boards are repaired on-site, and full replacements are cut and programmed where your car is parked - with the price agreed up front and no call-out fee.