Bought a Used Car With One Key, What to Do Next

Have the car read to find out how many keys it still accepts, have any you were not given deleted, then cut a spare. The order matters, because a spare cut first gets deleted with the rest.

One key is not a fault and it is not unusual. What it is, until somebody checks, is an unknown. The car itself holds the answer.

How many keys does the car have?

Every car built with an immobiliser keeps a list of the keys it has been told to accept. That list is held in the vehicle, not in the keys, and it does not change when the car is sold.

The list can be read. Plugged into the car, the right equipment reports how many keys are currently programmed to it, which is a number rather than an opinion.

That number is the whole answer to whether one key is a problem. A car that reports two programmed keys when you were handed one means a working key exists somewhere and you do not have it. A car that reports one means the previous owner genuinely had one as well, and the only thing missing is your spare.

Most cars carry slots for more keys than anyone uses, so a higher number than expected is common rather than sinister. It still needs knowing.

The reading is also the only part of this that is genuinely diagnostic. Everything a seller tells you about keys is recollection, and recollection across two or three previous owners is worth very little. The vehicle has no opinion and no reason to round the number down.

The reading takes minutes and needs no parts, which makes it the sensible first step rather than the last one. Everything else on this page depends on what it says.

One thing the reading does not tell you is who holds the other keys or where they are. That information exists nowhere, which is precisely why the answer is to remove the keys rather than to trace them.

Why one key is a security problem

A key that is unaccounted for is not the same as a lost key, and the difference matters.

Somebody holding a working key can open the car and drive it away without forcing anything. No glass, no damage, no alarm. To anyone looking, including a neighbour and later an insurer, it is a car that simply left.

There is no time limit on it either. A key sitting in a drawer works as well in two years as it does tonight, and the person holding it is under no pressure at all.

This is not usually about the previous owner. Keys go to garages, valeters, family members and previous partners, and the person who sold you the car often has no idea where the second one ended up. The risk comes from nobody knowing, not from anybody intending anything.

That is also why the answer is mechanical rather than a matter of trust. A key that has been removed from the car cannot start it, whoever has it and whatever they intended.

The same reasoning applies to a car bought from a dealer rather than privately. A forecourt car has usually passed through a part exchange, a transporter, a valeter and a workshop, and each of those is a place a key can stop travelling with the vehicle. The dealer is not concealing anything, because the dealer does not know either.

What deleting the old keys does

Key deletion is the step that closes this, and it is simpler than most people expect.

The car is instructed to forget the keys it currently accepts. The list is cleared and rewritten with only the keys physically present, so any key not in the room at the time stops working permanently. It is done at the vehicle, usually in under an hour, and the keys you hold carry on exactly as before.

Once a key is deleted from the immobiliser it will not turn the engine over. The car no longer recognises it as one of its own.

One honest limitation. Deletion stops a key starting the car. On a vehicle with a mechanical blade, that blade still opens the door afterwards, because the door lock is mechanical and knows nothing about the immobiliser. For most owners the car being undriveable is the whole of the concern. For anyone leaving valuables in it, that distinction is worth knowing before deciding this is finished.

Proof that the vehicle is yours is checked before any of this happens, which is the same protection working in your favour.

Delete first, then cut a spare

Almost every article on this subject says the same thing, which is to go and get a spare cut. That advice is right and the order is wrong.

Deletion clears the list. A spare cut and programmed before the deletion is on that list, so it is erased along with the keys you were trying to remove. The spare then has to be programmed a second time, and you have paid for the same work twice.

Done in the right order it is one visit. The car is read, the unwanted keys are cleared, and a second key is cut and programmed while the equipment is already connected.

That also makes the spare cheaper than it would be later, because a spare made while a working key exists is always less work than a key made when none does.

Check the blade opens the door

One check costs nothing and takes two minutes, and it catches a problem that only appears at the worst moment.

A blade that does not turn any lock usually means the key was made as a start-only key, or that the locks were changed at some point and the key was never matched to them. Either is worth knowing on the day you buy the car rather than in a car park in the rain.

Why used cars arrive with one key

Four ordinary explanations cover nearly every case, and none of them involve anything being hidden from you.

The spare was lost years ago. The owner replaced nothing because the car kept starting, and the missing key stopped being a thought long before the car was sold.

The spare broke and was never replaced. A snapped blade or a dead fob gets put in a drawer, and the cost of sorting it never quite justifies itself while one key works.

The car came through a trade route. Part exchanges, auction cars and ex-fleet vehicles frequently arrive at a dealer with one key, and the dealer sells it as it was received.

It only ever had one. Some vehicles were supplied new with a single key, particularly commercial ones and some lower specification models.

None of that changes what you do about it. It does change how much weight to put on the fact, which for most buyers is very little.

What one key does to the value

A missing key does reduce what a car is worth, and the reduction is predictable enough to plan around.

Trade buyers and online purchase services routinely deduct for it, because they must supply the second key before they sell the car on. The deduction is normally set at roughly what a replacement key costs them, and sometimes a little more to cover the inconvenience.

The useful consequence is that the money is not lost either way. Buying the spare yourself costs about what the deduction would have been, and you get the use of the key in the meantime. Selling privately, a car advertised with two keys attracts fewer questions and sells faster.

Where you are buying rather than selling, a single key is a fair thing to raise on price. It is a real cost you are about to carry, and most sellers know it.

Worth separating from all of that is the effect on insurance, which is none. No mainstream policy prices a car differently for having one key, and none of them require a spare. The cost of one key is a trade and resale matter rather than an insurance one, whatever a forecourt suggests.

Is it legal to sell with one key?

Yes, and that surprises people.

There is no requirement in a private sale to supply two keys or to volunteer that only one exists. A dealer is under no obligation to provide a second key either, unless the advertisement or the sales agreement said the car came with two.

Where the advert did say two keys, that is different. The car has not been supplied as described, and that is a conversation worth having with the seller promptly and in writing.

Where nothing was said either way and you noticed at handover, the practical position is weaker, because accepting the car with one key is generally taken as accepting the car. Raising it before money changes hands is worth far more than raising it afterwards.

None of that is a reason to walk away from an otherwise good car. It is a reason to price the second key into what you offer, and to get the reading and the deletion done in the first week rather than leaving it as a job for one day.

What to do in the first week

Four things, in this order, and the whole matter is closed.

Have proof that the car is yours to hand before booking, because it is checked on every job of this kind and a new owner with fresh paperwork is exactly the case the check exists for.