Keyless Entry Not Working? Causes and On-Site Fixes
Keyless entry usually stops working because the fob battery has weakened, and a keyless fob flattens one faster than an ordinary remote does because the car polls the key constantly rather than waiting for a button press. A fresh cell costs a few pounds and fixes most of them.
Where a new cell changes nothing, the answer is almost always in how keyless actually works, and it is not one system. Every door handle has its own sensor, and the aerials that look for your key outside the car are separate from the ones inside it.
That is why one door can stop while the others carry on, and why entry can fail on a car that still starts perfectly. Both are set out below, and neither means you need a new key.
Keyless Is Not a Remote, and That Changes Everything
Almost every article about a car key that has stopped working is about a remote with buttons on it. Keyless entry works in a completely different way, and the difference explains every fault on this page.
The handle senses your hand, the car wakes up and then goes looking for the key. Nothing is transmitted by you at all, which is why none of the advice about buttons applies.
A capacitive sensor in every door handle, each with its own wiring back to the car. They fail one at a time rather than together.
One set of antennas looks for the key around the outside of the car, another set looks for it in the cabin. They do different jobs and they fail independently.
The car asks and the key replies, many times a minute while you are near it. That constant conversation is what drains the battery.
The practical consequence is that keyless does not simply work or not work. It has several parts that fail separately, and which part has gone is usually obvious from the pattern rather than needing anything plugged in.
When Only One Door Stops Working
This is the most misdiagnosed keyless fault there is, and the answer is good news. If one handle responds and another does not, nothing is wrong with your key.
It proves the fob is transmitting, the car is listening and the system is healthy. Whatever is wrong is in the handle that does not respond and nothing else.
It is used far more than the others, so its sensor and the wiring in that door hinge see the most wear. That is why this fault is usually on the driver side.
Handle sensors sit in a part of the car that gets soaked constantly, and a corroded connector behind the handle is the commonest cause of a single dead door.
This is the fault that costs people the most, because the obvious move is to replace the key. A key that already works on three handles is not the problem.
A key that opens three doors out of four is a working key. It is transmitting, the car is receiving it, and the system is healthy. Replacing it costs money and changes nothing, because the fault is in a handle that is not asking the question in the first place.
The test takes ten seconds. Walk round the car and try each handle in turn with the key in your pocket, and note which ones wake up. That single piece of information changes what needs doing and what it costs.
When It Will Not Unlock but the Car Still Starts
Confusing until you know that the car has two separate sets of aerials, and then it makes complete sense. One set looks outside and one set looks inside.
The car sees the key inside the cabin, which is why it starts. That half of the system is working perfectly.
Whatever is going wrong is on the outside of the car, which narrows it to the handle sensors, the exterior antennas or their wiring.
A cell with just enough left for close range will be read at the start button and not from outside the door. This is the cheap version of the fault.
A key that starts the car but will not unlock it is a repair from £95 rather than a replacement. The car still recognises the key, so nothing has to be coded again.
This one is worth checking against a spare key before anything else. If the spare unlocks the car from outside, the first fob is transmitting too weakly and a cell will probably fix it. If the spare behaves the same way, the fault is on the vehicle and the keys are fine.
Why Keyless Fobs Flatten Batteries Faster
People assume a keyless key should last as long as an ordinary remote, and it does not. The reason is built into how the system works rather than being a sign of anything wrong.
A remote fob sits idle until you press it. A proximity key is polled by the car many times a minute whenever you are near it, and every reply costs power.
A keyless fob commonly needs a cell every eighteen months to two years, where an ordinary remote can run for four or five. That is normal rather than a fault.
The first sign is having to be closer to the handle than you used to be, or it working on the driveway and not across a car park. That is the moment to change it.
Coin cells lose voltage under load in low temperatures, so a cell near the end of its life fails on a January morning and works again by lunchtime.
So a keyless fob needing a cell more often than the remote on an older car is normal. What is worth noticing is the pattern before it stops entirely, because range fading is several weeks of warning and almost nobody acts on it.
The Fob That Has Gone to Sleep
A cause that did not exist a few years ago and now accounts for a steady number of calls. The key is working perfectly and has simply switched itself off.
A motion sensor inside the key puts it into a dormant state after a period of being completely still, and it wakes the moment it is picked up.
Relay thieves work by capturing the signal from a key sitting near a front door. A key that stops answering when left still gives them nothing to capture.
A car that worked on Friday and not on Monday, on a key that has spent the weekend in a bowl in the hallway, is almost always this.
Give it a shake and try again. If that works, nothing is broken and nothing needs fixing, which is worth knowing before anybody is called out.
It exists because of relay theft, where a signal is captured from a key sitting near a front door and repeated at the car. A key that goes quiet when nothing has moved it for hours gives a thief nothing to work with, which is why manufacturers added it. The keyless theft guide sets out what else helps.
Getting In and Getting Going Right Now
If you are standing at the car reading this, none of the diagnosis matters yet. A completely dead keyless fob still opens the car and still starts it, on almost every vehicle built in the last twenty years.
A catch or a slider releases a metal key hidden in the housing, and on many cars the driver door lock sits behind a small cover that pops off with a fingernail.
Opening a keyless car with the blade while the key is not detected often sets the alarm off. It stops as soon as the car reads the key at the start position.
Almost every keyless car reads a chip in the key with no battery at all, at very close range. Press the fob flat against the button and press it.
A marked place on the steering column, the bottom of a cupholder or a slot in the console. The handbook names it and it usually carries a small key symbol.
The reason the second half works is that the remote buttons need power and the chip inside the key does not. That chip is woken by the car itself at a range of a few centimetres, which is exactly why holding a flat fob against the start button gets the engine going.
What It Costs to Put Right
Six outcomes, and the cheapest of them is not a job at all. Working down from the top is worth doing before anybody is called.
Prices are from, at your vehicle, with no VAT and no call out fee. The first row is not a job at all and it is still the right place to start.
Most keyless calls end in one of the middle two rows rather than a new key. A fob that the car still recognises is repaired or resynced rather than replaced, and a spare smart key taken while the first one works is always cheaper than one taken later. Full pricing sits on the car key replacement cost guide.
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