Your New Key Worked, Then Stopped: What Went Wrong and Who Pays

A key that failed on day one is a bad key. A key that worked for a fortnight and then quit is a different and more interesting problem, and the cause is almost never random. It points at a short list of specific things, and which one you have decides whether the fix is free.

This is also the situation where owners most often pay twice: once for the key, and again for a second visit that should have been covered. Working out what failed, before you call anyone, is what prevents that.

First, the test that splits the problem in half

Before anything else, use your other key.

If you have a second key that still works, take it to the car and try it under the same conditions that make the new key fail. Cold morning, same car park, same driver door.

Old key works perfectly, new key fails. The fault is very likely in the new key or in how it was programmed. That is the situation this article is about, and the sections below sort out which of the four causes it is.

Both keys fail in the same way. The vehicle is much more likely to be the problem. Two keys do not usually fail in the same week, and a car that rejects everything is describing a fault in the immobilizer, its aerial, or the vehicle battery rather than a fault in a key. One key works and the other does not covers how to read that split, and a car that starts then dies immediately covers the specific immobilizer pattern.

If you have no second key, the substitute test is the backup position. On a push-button car, hold the fob against the marked spot on the column or console and try to start. If the car starts that way, the immobilizer chip inside the fob is alive and the radio side is what failed, which narrows things considerably.

Cause one: it was cloned, not programmed

This is the most common explanation for a key that works and then quietly stops, and most owners do not know the distinction exists.

A programmed key is registered into the vehicle key list as a new, separate entry. The car knows it as its own thing.

A cloned key copies the identity of a key the car already accepts. The vehicle cannot tell the copy from the original, because as far as it is concerned there is only one key.

Cloning is legitimate, fast and cheap, and on plenty of older vehicles it is the sensible choice. But a clone has no independent existence in the car's memory. If anything later causes the vehicle to rebuild or re-verify its key list, the clone can be the entry that disappears. The original still works. The copy does not.

How to tell. Two clues. Cloning is usually noticeably faster and cheaper than programming, so a job that took ten minutes and cost much less than the quotes you were given elsewhere was probably a clone. And a cloned key cannot normally be programmed to have its own separate functions, so if the new key had to behave exactly like the old one in every respect, that is consistent.

What to do. Ask directly whether the key was cloned or programmed. If it was cloned and it has failed, the fix is usually to program it properly, which is a different procedure rather than a repeat of the same one.

Cause two: a marginal aftermarket fob

An aftermarket fob can program successfully and still be a poor key.

Programming proves the car accepted the chip during the appointment, in ideal conditions, with the fob held near the aerial. It does not prove the transmitter is strong, the chip is well seated, or the board tolerates temperature and vibration. A fob at the edge of acceptable range works on the driveway on a mild afternoon and fails in a cold car park three weeks later.

How to tell. Range is the signal. If the new key needs to be closer than the old one to do the same job, and that distance has been shrinking, the fob is weak rather than dead. A fob that only works up close walks through the range test in detail.

What to do. This is a parts failure. It belongs to whoever supplied the part. If you supplied it yourself, the position is different and less comfortable, which is exactly what buying your own key fob online covers.

Cause three: the cell in a new fob was not new

A replacement fob can sit in a warehouse for a long time, and the coin cell inside it ages on the shelf.

A cell that was already two years into its life when the fob was fitted has correspondingly less life left, which can be weeks rather than years. The failure pattern is identical to the weak-fob pattern above: shrinking range, then nothing.

How to tell. Fit a fresh cell. It costs a few dollars and settles the question immediately. If a new cell restores normal range, the fob is fine and the cell was the problem.

What to do. Worth mentioning to the shop, but not usually worth a dispute. It is the cheapest possible outcome and the quickest to test, which is why it is worth ruling out before making a phone call.

Cause four: the car was already failing

This is the uncomfortable one, and it is more common than people expect.

An immobilizer aerial, the ring or coil around the ignition or the antenna behind the dash on a push-button car, can degrade gradually. So can an ignition cylinder. So can a vehicle battery. All three produce intermittent, weather-sensitive, hard-to-reproduce symptoms that look exactly like a failing key.

That is why the sequence often runs: the car misbehaves, the owner concludes the key is worn out, a new key is bought, the car behaves for a while, and then the same symptoms return. The new key did not fail. The underlying fault was never the key, and the new key masked it briefly because a fresh chip and a fresh cell have more margin than a worn one.

How to tell. The both-keys test at the top of this article is the strongest indicator. Beyond that, look for symptoms that are not about the key at all: dashboard warning lights, a slow crank, an engine that starts and immediately dies, or behaviour that tracks temperature rather than which key is in your hand.

What to do. This is diagnosis rather than key replacement, and it is reasonable for it to be charged as new work. What is not reasonable is being sold a second key for the same fault.

The fifth cause: your car ran out of key slots

This one is rarer than the four above but it explains a specific and confusing pattern, so it is worth knowing.

Vehicles hold a finite number of keys in memory, commonly somewhere between four and eight depending on the platform. When that ceiling is reached, adding another key means something has to give, and different manufacturers handle it differently. Some platforms refuse the new key outright. Others erase the whole list and re-register only the keys physically present at the appointment.

The pattern to recognise: a household with several keys accumulated over years, a new key added, and then a key somewhere in the house stops working. Nothing failed. The car did exactly what it was designed to do, and the key that stopped is simply the one that was not in the technician's hand at the time.

This is the reverse of the situation this article is about, but it lands in the same phone call, which is why it belongs here. If the key that stopped is an old one rather than the new one, look at slot behaviour before suspecting workmanship. And when you next have key work done, bring every key you want to keep, including the spare in the kitchen drawer and the one an adult child has. It costs nothing at the time and it is not recoverable afterwards without a second appointment.

Who pays for the second visit

The recognised standard for automotive locksmith work is a ninety-day workmanship warranty. A key that stops working within days or weeks of being programmed is about as clear a warranty case as exists.

The honest dividing line:

What failed	Who it belongs to
Programming did not hold, or the key was cloned when it needed programming	The shop, inside the warranty window
A supplied fob or chip is faulty or weak	The shop, as a parts failure, if they supplied it
A fob you supplied yourself is faulty	You, which is the risk you took on price
The vehicle has a separate developing fault	New work, reasonably chargeable
A coin cell has gone flat	Nobody, practically speaking. It is a few dollars

Two sentences make the conversation straightforward. Call the shop that did the work first, not a different one, because a second shop has no obligation to honour someone else's warranty and every reason to sell you a new key. And ask them to tell you which row of that table they think you are in before they arrive, so the money question is settled while it is still a conversation rather than an invoice.

What to have ready when you call

• The original invoice, with the date and what was supplied.
• Whether the key was cloned or programmed, if it says. If it does not, that itself is worth asking about.
• The result of the other-key test. This is the most valuable thing you can offer, because it tells the shop which half of the problem to bring equipment for.
• Whether a fresh coin cell changed anything.
• When exactly it stopped, and whether it was gradual or abrupt. Gradual points at the fob or its cell. Abrupt points at programming or the vehicle.

A shop that hears all five of those can usually tell you on the phone whether they are coming out under warranty or quoting new work, which is a much better outcome than finding out in your driveway.

Preventing the repeat

Three things make this far less likely next time.

Ask what you are buying. Cloned or programmed, original equipment or aftermarket, and what the warranty is. The answers take thirty seconds and they are the difference between a key and a lottery ticket. What a legitimate shop asks for covers what a straight operator sounds like.

Get a real invoice. Vehicle identification number, year, make, model, key type, part numbers, warranty terms. Our guide to what the VIN changes about your quote explains why that number matters more than any other piece of information about your car.

Test the new key properly before the technician leaves. Not once, in the warmth, immediately after programming. Lock and unlock from a distance, start the car, switch everything off, wait a few minutes so the systems settle, and start it again from cold. Six things to do when you get a new key is the full checklist, and it exists precisely because the five minutes before someone drives away is when problems are cheapest to catch.

If you have worked through this and need a specialist for your vehicle, get help and we will match you with one equipped for your make. If the original shop is not responding and you would rather understand your options first, who can actually program a car key sets out all five routes and what each is realistically good for.

Warranty terms described here reflect the ninety-day workmanship standard common in the automotive locksmith trade as of September 2026; the terms that bind are the ones on your own invoice. Cost ranges referenced are the bands published across CarKeyNation's service and make pages.