Two jobs in one key
On most vehicles built in recent decades, a key does two separate jobs. The metal blade has to match the lock's internal pattern so it can turn. The hidden chip in the head has to carry a code that the car's security system accepts. A duplicate that does only one of those jobs will fail.
If the blade is wrong, the key will not enter smoothly, will not turn, or will turn only with force. If the chip is wrong, the key can feel perfect in the lock, even turn the ignition, and still the engine will not start or will start for a second and die.
Knowing which job failed is the first step in fixing the copy. The symptoms are different enough that a few minutes of careful observation can usually tell you.
Think of it as a door with two guards. The first guard checks the shape of the key, the second checks the secret handshake. A copy has to satisfy both. Many problems with duplicates come from satisfying only the guard that is easier to impress, which is the shape. Keep this picture in mind as you read the rest of the page, because every symptom below traces back to one of the two guards saying no.
When the blade is the problem
Blade problems come from cutting. A machine traces the original and cuts the blank, and errors can appear at several stages. The blank may be the wrong profile, the cutting wheel may be worn, the original may be so worn that it passes along its own errors, or the cut may be slightly deep or shallow in one spot.
Signs include a key that does not slide in fully, one that sticks halfway, one that turns in the door but not the ignition, or one that works only if you lift or press at an angle. The key may also work for a few days and then get stiff as it wears into the lock.
Holding the copy and the original side by side in good light can reveal differences. Look at the length, the shoulder where the key stops, the groove pattern along the side and the depth of each cut. Even small differences matter on a high-security design.
Why worn originals make weak copies
If the original is rounded and loose in the lock, a copy traced from it inherits that looseness. Cutting by the vehicle's code or by decoding the lock can give a cleaner result. That is one reason technicians sometimes prefer not to copy a very worn key. See a worn key that barely turns for more.
When the chip is the problem
A key with a transponder chip needs the chip's code to be registered with the car. Hardware counters often cut the blade without programming the chip, so the copy opens doors and turns the ignition, yet the engine will not start. Some copies carry a blank chip that was never written to match the car.
Another version involves chips that cannot be cloned. Some systems use encrypted codes that cannot be copied by a simple device. For those, the copy must be added to the car through programming, with the vehicle's computer, not duplicated chip to chip.
The result is the same: a key that fits the lock and fails the car. A security light that stays on, flashes or comes on only when you try to start is a typical sign. Our page on transponder keys explains the difference between cutting and programming.
- Opens doors and turns the ignition, yet the engine will not start.
- Security light stays lit or flashes during a start attempt.
- Engine cranks and dies after a second or two.
- Original key works normally.
Remote buttons that do not respond
Some copies are meant to include remote buttons for locking and unlocking. A remote function needs its own programming, separate from the chip that allows starting. A key may start the engine and still have dead buttons, or have working buttons and no start.
The remote may also lose sync after a battery change, a dead battery or a long period without use. Sometimes the copy was programmed with the wrong frequency or the wrong type of remote chip for the car.
It helps to test each function separately: the lock, the ignition, the start, and each button. Notes about what works and what does not give a technician a precise starting point, and are worth writing down before you call.
Mistakes to avoid before you call
The natural reaction to a failing copy is to try again and again. Resist it. Forcing a poorly cut blade into a lock can scratch the pins and wafers and leave a mark that the original now has to live with. It can also snap the new key off in the ignition.
Do not file the new key to fit, unless you know exactly what you are doing. Filing removes metal that cannot be put back, and an accurate fix usually means cutting a fresh key.
Do not return to the original seller and use the same machine again without describing the problem clearly. Ask what blank, code and chip were used, so that the next attempt is not a repeat of the first.
- Do not force the copy into the lock or the ignition.
- Do not file or bend the blade to make it fit.
- Do not keep cranking the engine with a key that does not start it.
- Do not throw away the failed copy, since it is useful evidence.
Testing the copy methodically
A short, calm test routine gives you facts to share. Work with the car in park, parking brake on, and the engine off. Start with the driver door and see whether the key slides in all the way and turns smoothly. Then try the trunk or any other lock that uses the same key, if your vehicle has one.
Next, try the ignition. Does it enter fully? Does it turn to the accessory position? Do the dash lights come on? Does the security light behave the same way as with the original? Then try to start the car and note exactly what happens.
Finally, try the remote buttons from a short distance. Keep the results in a short list so you can read them out. This is the information a service or technician will ask for.
Reading the results
If the key will not enter the door lock but fits the ignition, or the reverse, the blank may be the wrong shape for one of the two cylinders, a problem that sometimes shows up on vehicles that use different keyways for the door and the ignition. If it enters everywhere but turns nowhere, the cuts are likely wrong.
If it turns everywhere but the engine does not start, think chip. If the engine starts and the remote is dead, think remote programming. If everything works but the key feels rough, the cut may be rough or the original may be the source of wear. Each result points in a different direction, which is the whole value of testing in order.
Take a clear photo of both keys lying flat next to each other, with the cuts visible. A technician can learn a lot from that picture even before arriving, such as whether the blank looks like the correct style.
A closer look at what can go wrong with the cut
Key cutting looks simple from the counter, but several small variables can undo it. The first is the blank itself. Many vehicles share similar-looking blanks that differ by a millimeter in width, shoulder position or groove shape. A blank that is almost right can still fail to enter or turn.
The second is alignment. A key has to be clamped in the machine at the exact same position as the original. If the clamp sits slightly off, every cut is shifted, and the copy feels loose or tight. The third is depth. High-security keys with cuts on the side need precise depth and spacing, and a worn cutter can leave rough edges that bind.
None of these is a mystery to a trained technician, and each can be corrected. The fix may be as simple as recutting on a calibrated machine, or as simple as selecting the correct blank. What matters is that you do not assume the vehicle is at fault when the key has not been made properly.
- Wrong blank profile or length.
- Key clamped off position in the machine.
- Cutter worn or cuts not deep enough.
- Burrs left on the blade that catch inside the lock.
- Code or decoding data entered incorrectly.
A short story of two copies
Imagine two drivers with similar sedans. The first has a copy cut from a ten year old key. The copy slides in, turns in the door and starts the car, but it feels gritty and sticks in the ignition by the end of the month. The original was worn, the copy inherited the wear, and the lock suffered. A fresh cut by code would have been smoother.
The second driver has a nearly new key, and the copy fits like the original, but the engine will not start. The chip was never programmed. A visit from a technician with the right equipment fixes it in a single visit, and the key then works for years. The blade was never the problem.
Same complaint, two causes. That is why the order of tests matters, and why describing the symptom precisely makes a real difference to how a technician prepares.
Using the original wisely while you sort it out
While you wait for a fix, treat the original as precious. Keep it off the heavy key ring, store it in a secure place when you are not driving, and avoid lending it out. Do not leave it in the car, where a locked-out moment can turn a minor annoyance into a larger one.
If you must drive, let the original do all the work. Do not alternate between the original and the failing copy, since swapping keys in and out of an ignition many times adds wear for no reason.
If you have a long trip planned, think about solving the duplicate problem before you leave. A trip is the wrong time to find out that your backup key does nothing. A key in the glove box is only helpful if it works.
What a mobile technician can do about a bad copy
A mobile automotive locksmith comes to the vehicle. You begin with a call or callback request, and the service asks for year, make and model, location, and what the copy does. Details about where and how the duplicate was made are useful.
Availability, coverage and terms are confirmed before a technician is dispatched. This page is educational and creates no service agreement. On site, ownership or authorization is checked, and then the technician evaluates the copy against the car and the original.
Possible outcomes include recutting the blade, replacing the blank with the correct one, programming the chip, programming the remote, or telling you honestly that the copy is not usable and a different key should be made. Limits depend on the vehicle, and newer vehicles from some makes may need dealer-level tools or manufacturer access.
Cut by code or cut by copy
There are two broad ways to make a key. One is copying, where a machine traces an existing key. The other is cutting by code, where the cut pattern comes from information tied to the lock, such as a key code, or from decoding the lock itself. The second can produce a more accurate result when the original is worn.
A technician who works with vehicles often has access to code data and decoding tools for many models, though not all, and the available approach depends on the vehicle. If your original is worn, asking for a code-based cut can help.
The difference between the two methods is a good reason to treat a failing duplicate as a symptom, not a mystery. Often the copy was fine as a tracing and the original was the weak link.
Ownership proof for a corrected key
Even for a repair of a copy, a reputable service asks for proof that you own the vehicle or are authorized to use it. A new key is access to the car, so verification applies every time. Bring identification and registration or title.
For a rental, company or family vehicle, bring the document or message that shows your authorization. Our ownership proof guide lists common documents.
The check happens on site before work begins. It is routine and it protects you.
How to get a copy that works the first time
Preparation helps. Bring the healthiest key you have, not the most worn one. Tell the cutter the year, make and model so the right blank and chip are chosen. Ask whether the copy will be programmed to the car, not just cut.
Ask for the key to be tested in the lock and in the ignition before you pay or leave. If a service cuts the key, it should be willing to confirm that it opens, turns and starts the car. Never accept a duplicate for an immobilizer vehicle that has only been cut.
Our spare key guide covers planning, and the page on car key replacement explains the larger picture.
Why timing matters
The ideal time to fix a duplicate is while you still have a working original. The car can authorize the new key from the existing one in many cases, which simplifies things. If the only working key then fails, the work becomes an all keys lost job.
If your copy is your only extra key and it does not work, treat the original as your last working key and protect it. Avoid taking it on risky outings, and do not hand it to a valet or a friend if you can avoid it.
If both keys fail someday, the page on all keys lost explains what to expect.
Related situations
Duplicate trouble often connects to other key problems. A fob that loses range can look like a copy that failed, and a key that has been through the wash can lose its chip long after it was made. When in doubt, work through the symptoms one at a time rather than assuming the most recent change caused the problem.
If the copy turns but the car will not start, read key turns but the car will not start. If a key blade is worn rather than newly cut, see worn key that barely turns. For a wider view of problems, visit the situations hub.
If a child or pet is locked in a hot car, call 911 first. Everything else can wait.
Common questions
Why does my duplicate key turn but not start the car?
The blade is probably cut correctly, but the transponder chip has not been programmed to the car. Many vehicles will not start unless the chip is registered. The security light on the dash often stays on or flashes when this happens.
Can a badly cut duplicate damage my lock?
It can. A poorly cut blade can scratch or wear the pins and wafers, especially if forced. Stop using a copy that does not turn smoothly and have it checked before it leaves marks.
Is the copy bad, or is my original just worn?
Either is possible. A worn original can pass its rounding to a copy. Compare the two keys side by side, and try a fresh cut made by code. A technician can decide which is the cause.
Do remote buttons need separate programming?
Often yes. The start function and the remote functions are separate. A copy might start the car with dead buttons, or have working buttons and no start. Test each function and report which ones fail.
Can a failed duplicate be fixed or must I start over?
Often it can be recut or programmed. Sometimes the blank is the wrong type and a new key is the better choice. A technician will tell you after testing the key against the car.
What should I have ready when I call?
Year, make and model, where the vehicle is, which functions work, where the copy was made and whether you still have a working original. Availability, coverage and terms are confirmed before any technician is dispatched.