Car Key Fob Not Working? Six Causes and the Fixes
A car key fob usually stops working because the battery inside it has died, and a fresh cell fitted the right way up fixes most of them in about two minutes. That is the first thing to try and it costs a few pounds.
The harder question is what to do when the battery is not the answer, which is where most people reading this already are. Five other causes account for the rest, and one of them is not a fault in the key at all. A fob that has lost its pairing is not a broken fob and does not need replacing.
Before any of that, there is a way into the car and a way to start it with a completely dead fob. That comes first, because standing next to a locked car is not the moment for a diagnosis.
First, Get Into the Car and Get It Started
A completely dead fob still opens the car and still starts it, on almost every vehicle built in the last twenty years. Both routes are built in and neither needs a working battery.
Almost every keyless fob hides a metal blade, released by a small catch or slider on the back. It opens the driver door, sometimes through a cover on the handle that pops off with a fingernail.
Opening a keyless car with the blade while the fob is dead often sets the alarm off. It stops as soon as the car reads the key at the start position.
Most keyless cars will read a chip inside the key with no battery at all. Press the fob flat against the start button and press, and it fires.
A marked position on the steering column, the bottom of a cupholder or a slot in the centre console. The handbook names it, and it is usually drawn as a small key symbol.
The remote buttons need power and the chip inside the key does not. That chip is woken by the car itself at close range, which is why a dead fob held against the start button still starts the engine. It is designed in as the backup, not a trick.
Once the car is running, the diagnosis can wait until it is somewhere sensible. Everything below can be worked through on a driveway rather than in a supermarket car park in the rain.
The Six Reasons a Fob Stops Working
In order of how often they turn up, cheapest first. The first two are fixed at home, the next three need somebody with equipment, and the last one is not a fault at all.
How it shows Range drops off first. The fob works with the key touching the door and not from across a car park, then stops entirely.
The fix A fresh CR2032 or CR2025, fitted the same way up as the old one. Two minutes and a few pounds, and it is the answer roughly three times in four.
How it shows A brand new battery changes nothing at all, and the fob shows no sign of life whatsoever.
The fix Two causes. The metal contact arms get bent flat by repeated battery changes and need easing back up, and many coin cells carry a bitter anti swallow coating that insulates the contact. A wipe with alcohol on the flat face clears it.
How it shows The battery is definitely good, the buttons click, and the car ignores it. Often it happens straight after a battery change.
The fix The fob needs resyncing to the car. A few models resync from the driver seat with a sequence in the handbook, and most now need the diagnostic port. Nothing is broken and no new key is needed.
How it shows It worked for a few days after a soaking or a hard drop, then became unreliable and finally died.
The fix Dry it out immediately and have the board cleaned before corrosion spreads. Caught early this is a clean and reflow. Left for weeks it becomes a new fob.
How it shows One button stops responding while the others still work, or a button needs pressing hard and in exactly the right spot.
The fix A button membrane replacement. The electronics are untouched, so nothing needs coding again and the original key keeps working throughout.
How it shows The fob fails in one particular place, usually a multi storey, a busy car park or near a mast, and works perfectly elsewhere.
The fix Move a few metres and try again, or hold the fob against your chin so your head acts as an antenna. If it only ever fails in one spot, the fob is fine.
Work down that list rather than across it. Most people who end up buying a new fob never tested the three above the one they assumed they had.
The Battery Is New and It Still Does Not Work
Three things cause this, and two of them cost nothing to rule out. Check the contacts and the coating before assuming the fob is finished.
The contact arms inside the case get flattened a little by every battery change, and eventually they no longer press hard enough against a fresh cell to make a circuit. Easing them up a fraction with a small screwdriver brings the fob straight back to life. Separately, many coin cells now carry a bitter coating on the flat face to stop children swallowing them, and that coating does not conduct. A wipe with alcohol on the face before fitting removes it.
If both of those check out, the fob has lost its pairing with the car. That is a resync rather than a replacement, and it is the single most common reason a perfectly good fob gets thrown away. Key programming covers what the equipment actually does.
When Both Fobs Stop at Once
Two independent fobs failing together almost always means the fault is in the car, not in the keys. That single distinction is worth several hundred pounds, because the obvious move is to buy new keys and the obvious move is wrong.
The commonest cause by a distance. A car battery too weak to run the receiver properly will ignore both fobs while still having enough left to look alive on the dashboard.
One receiver serves every key. When it goes, every key stops at the same moment, which is exactly the pattern that makes people suspect their keys.
Aftermarket alarms, trackers, dashcams and cheap USB chargers all sit close to the receiver frequency. Unplugging a recent addition is a free thirty second test.
It happens only where both were soaked or both carry cells from the same tired packet. Everything else on this list is more likely first.
Unlock the car with the blade, start it with the fob held against the start button and let it run for fifteen minutes. If both remotes come back afterwards, the vehicle battery was the problem all along and neither key ever needed touching.
Where the receiver itself has failed, the diagnosis happens at the vehicle and the keys are proved good before anything is ordered. Buying two replacement fobs for a receiver fault leaves you with two more keys the car still ignores.
When It Works Sometimes and Not Others
Intermittent failures are a separate problem from dead ones, and the pattern gives the answer. Where and when it fails matters more than what it does.
A fob that fails only in one location is dealing with interference and is not faulty. A fob that fails when cold has a cell near the end of its life, because coin cells lose voltage under load in low temperatures and recover when warm. A fob that needs a hard press on one button has a worn membrane. A fob that works after being squeezed or tapped has a cracked solder joint inside, which is a repair rather than a replacement provided it is dealt with before the joint breaks completely.
Noting the pattern for a couple of days costs nothing and usually settles it. An intermittent fault diagnosed properly is a £95 repair, and the same fault ignored becomes a car that will not open on a morning when it matters.
What Each Fix Costs
Four figures cover every outcome on this page, and the gap between the top and the bottom of them is the reason it is worth working through the list in order.
Three to eight pounds from any supermarket or hardware shop. Worth doing before calling anybody, because it is the answer most of the time.
From £95 at the vehicle with no VAT, whether the fob needs pairing again, a new membrane and case, or replacing outright.
From £65, without damage, where the emergency blade is not enough or the blade itself has been lost.
Roughly £250 to £1,000 with VAT on top, and the car usually has to get there. That is the figure most published advice still points people towards.
Most published advice about key fobs still ends by suggesting a main dealer, which is how the £250 to £1,000 figure became the one everybody expects. A resync, a membrane, a case or a replacement remote are all done at the vehicle in Leeds from £95, with no VAT and no call out fee, and the car does not move. Attendance across the LS postcodes runs at about 30 minutes.
Questions About Key Fobs
DBS checked · Fully insured · Autel IM608 Pro II, ABRITES, Smart Pro and Xhorse Condor on every job · No VAT · All Leeds LS postcodes · 07724214298
New Battery In and Still Nothing?
Resync, repair or replace at your vehicle from £95, no VAT.
All makes covered. All Leeds LS postcodes. No call-out fee.