Key not recognised or car won't unlock: VW and Audi

Your key does two completely separate jobs, and they fail independently. One is the radio remote that locks and unlocks the doors, which runs off the little battery in the fob. The other is the immobiliser transponder — a passive chip in the key that the car reads from a few centimetres away, and which needs no battery at all. Most "key not recognised" problems land in one of those two boxes, and a fair number land in a third: a tired 12-volt battery in the car itself, which does a convincing impression of both. Working out which of the three you have takes about two minutes and costs nothing, so start there rather than buying anything.

First, split the problem in two

The remote is a radio transmitter. It has to reach the car from several metres away, so it needs a healthy fob battery, working buttons and a working receiver in the car. The transponder is different: it is a passive chip with no battery, woken up by an electromagnetic field from a reading coil around the ignition barrel — or, on keyless cars, from a marked spot that is often the start button itself, and on other models the steering column or the centre console. The handbook shows where. It works over a couple of centimetres and it does not care whether your fob battery is flat.

Because they are separate, the symptom tells you which one has broken. Ask yourself three questions, in this order: does the car respond to the button, does the engine start and keep running, and does your other key behave exactly the same way? Those three answers put you in one of the boxes below, and everything after that is confirmation rather than guesswork.

• Remote does nothing, but the car starts and drives normally once you're in — this is the radio side. Nothing is wrong with the immobiliser.
• Doors lock and unlock fine, but the engine cranks and won't fire, or fires and dies after a second, usually with a key or car-and-padlock symbol lit or flashing in the dash — this is the immobiliser side.
• Neither key does anything at all — suspect the car, not the keys, and start with the car's own 12-volt battery.
• A keyless car that has stopped noticing you approach — most often the fob battery, sometimes the car's battery, and sometimes nothing more than a fob sitting in a signal-blocking wallet or pouch. There is a backup way in and a backup way to start it; both are in the handbook.
• The engine cut out while you were driving — that is not the immobiliser, and it is the one version of this that is genuinely unsafe. Go straight to "When to stop and call recovery" below.

Rule out the cheap and boring causes before you spend anything

A tired 12-volt battery in the car causes an astonishing amount of odd electrical behaviour, including central locking that half-heartedly clunks, keyless entry that ignores you, and immobiliser faults that aren't really immobiliser faults. If the car has been standing, if it cranks slowly, or if it has recently been jump-started, get the battery properly charged and tested before you diagnose anything else. This single step accounts for a great many "the key has failed" calls.

Then try the free tests. They cost nothing and each one rules something out, which is the whole point — you are shrinking the list, not collecting possibilities.

• Try your spare key — for both jobs. Unlock with it, then start with it. This is the single most useful test you can do.
• Take the key off the keyring and try it alone. Other transponders — a second car key, a work fob, a mass of metal — can shield or confuse the reading coil.
• Try somewhere else entirely, a few streets away. If the remote only fails at home, at work or in one car park, that is radio interference, not a fault.
• Unplug anything recently added: cheap USB chargers, dashcams and some aftermarket LED bulbs throw out radio noise that can swamp the receiver.
• Stand right next to the car and press again. Working at arm's length but not across the car park is a weak signal, not a dead one.

When the remote is the problem

Start with the battery, but do it properly. Fit a fresh cell of the type printed on the one you take out, check it is the right way up, and look at the metal contacts — corrosion, or a tab that has lost its spring, will stop a brand-new battery working. Many fobs have a small LED; if it is dim or dead with a known-good cell, the fob's own electronics or its battery contacts are at fault.

Which buttons fail is a strong clue. If lock works and unlock doesn't, or one button only responds when you press it hard and in a particular spot, that is a worn micro-switch or a perished rubber pad inside the fob, not a car problem. If the key has been dropped hard, sat on, or been through the wash, a cracked solder joint or water damage is likely, and the symptoms are often intermittent.

The good news is that a fob is often repairable. Replacement switches and shells are widely available, and provided the original circuit board and transponder are carried across into the new housing, nothing has to be re-taught to the car and it will still start. Replacing the electronics themselves, rather than just the housing, is a different job and does need adapting — so ask which one you are being quoted for. Get the work done by someone who knows the fob rather than forcing the case apart yourself if you are not confident, and check whether the blade needs transferring or cutting.

One more thing worth knowing: a remote can drop out of step with the car after a long spell unused, or after a lot of button presses well out of range. The re-sync method varies by model — it is usually something simple involving the driver's door barrel or switching the ignition on — and your handbook will list the one for your car.

When the car ignores both keys

Two keys failing at once points at the car. The receiver aerial is a common culprit: depending on the model it may be built into the central convenience module, or be a separate aerial near the rear screen, the roof aerial base or the interior mirror. A damp connector — after a boot leak, a blocked sunroof drain or windscreen work — gives exactly this symptom: everything else in the car is fine, but the remote has short range or none at all. The exact location varies by model and year, so don't start pulling trim on a guess; the stored fault and live data will tell you where to look.

Watch what the car actually does when you press the button. If the indicators flash and you hear most of the doors clunk but one stays put, that door's lock module or its latch is the fault, and the remote is fine. If the alarm has also started going off by itself, or the interior light behaves oddly, you are in the same family of faults. On some older models the central locking is vacuum-operated, and a leak shows up as the pump running on and on instead of stopping.

A blown fuse for the convenience system will also take out everything at once, so it is worth a look before anything more involved.

When it unlocks but won't start: the immobiliser

If the doors work and the engine turns over normally but won't fire — or catches for a moment and dies — the immobiliser has not accepted the key. There is usually a symbol in the cluster to confirm it, and on cars with a display you may get a message about the key.

Try the spare. If the spare starts it, the first key's chip or its position in the housing is at fault: chips crack, and a copied blade sometimes gets cut without the original chip being transferred. If neither key starts it, look at the reading coil around the ignition barrel — a broken wire or an unplugged connector there is common — or at low battery voltage, which causes plenty of false immobiliser lockouts, particularly after a jump start.

Don't sit there cranking it. Repeated attempts flatten the battery you may well need, and on a petrol engine can wet the plugs and make matters worse. Two or three tries is enough to know.

It is worth saying plainly what an immobiliser is designed to do: stop the engine being started. It is not designed to shut an engine down once it is running. So if your car died at speed rather than refusing to start, stop treating this as a key problem — that is a different fault, and a potentially serious one. See the next section.

And don't let anyone talk you into an "immobiliser bypass" box, or into having the immobiliser deleted, as a way around a key fault. It strips the car of its theft protection, it is very likely to matter to your insurer, and it does not fix whatever was actually wrong. Legitimate dealers and locksmiths won't do it.

When to stop and call recovery

Most key faults are an inconvenience rather than a danger — a car that won't start is a parked car, and a parked car is safe. A short list of things that turn up around this fault are not, and they all end the same way: stop, don't drive it, get it recovered and looked at. If any of these apply, the diagnosis above can wait.

• The engine cut out while you were driving, or has cut out on the move before. When an engine stops, the brake servo usually has assistance left for only a couple of pedal presses and the power steering assist goes with it, so the car becomes very heavy to stop and steer. Do not carry on driving to see whether it happens again.
• The steering wheel is locked and will not release. Some VAG models use an electric steering column lock, and it can fail. Never try to move, tow or push a car with the steering locked.
• A brake, steering, airbag or engine-management warning light has appeared alongside the key problem — or the engine light is flashing. That is a separate and higher-priority fault. A flashing engine light in particular means stop as soon as it is safe to do so, rather than driving on.
• You can smell fuel, or anything is hot, smoking or smells of burning around the ignition switch, steering column or fusebox. Don't crank it again. Get out and get help.
• It's late, you're somewhere isolated, and the car can't be secured properly. Calling recovery is a sensible decision, not a defeat.

Getting in and getting home right now

Every VAG key has a metal blade. On a flip key it swings out at the press of a button; on a keyless fob it is an emergency blade hidden inside the body, released by a catch or a small slider. On models with no visible lock on the driver's door, there is a barrel behind a cap on the handle — the handbook shows how the cap comes off, usually with the blade itself.

Expect the alarm to sound when you open the door that way, if it was armed. It normally stops once the ignition is switched on with the key, or once you press start with the fob held against the marked spot. On keyless cars, that same marked spot is the backup start method when the fob battery is dead — the car reads the passive chip at close range exactly as a bladed key would.

If you have to leave the car locked with the blade key only, be aware that on many models this does not arm the alarm or deadlock the car; the behaviour varies. Treat it as less secure than usual, take your documents and anything valuable with you, and if you are somewhere isolated or it is late, calling recovery is a perfectly sensible decision. And whatever you do, don't hide a spare key on or under the car.

What the stored fault code adds

This is where guesswork stops. The modules involved log what they actually saw, and that usually settles the argument in one reading. The central convenience module will tell you whether it received a button press at all. The immobiliser — which on many models lives inside the instrument cluster, and on others in the body control module — will say whether it saw a key, and whether the key it saw is one it has been taught to accept. Those are two very different faults with the same symptom, and no amount of pressing buttons in a car park will separate them.

The live values matter as much as the codes. Watching the receiver while you press the fob shows instantly whether the signal is arriving; the door modules show each latch and lock switch changing state as you operate them; and the immobiliser will show how many keys are currently adapted, which tells you whether that online-bought fob was ever learned. That is the difference between replacing a receiver aerial and replacing a key you didn't need to buy.

That is the job VAGPULSE is built for: the Windows software and cable on this site talk to the convenience, door and immobiliser modules on a VW, Audi, Skoda or SEAT, show you those live values as you press the button, and read out the stored codes, for a single payment. Cutting and adapting an actual key still goes through the ownership-proof route described below.

Replacement keys, and what adaptation really means

A new key is two separate jobs. The blade has to be cut to your locks, and the electronics have to be taught to your car: the transponder adapted so the engine will start, and usually the remote learned so the doors respond. A key that has not been through that second step will open the door mechanically and do nothing else — which is why an uncut, unadapted fob bought online is not a fix on its own.

On modern VAG cars the immobiliser data is protected, and adaptation goes through a documented route that requires proof that the car is yours. That means a franchised dealer or a properly registered auto locksmith, and it is entirely routine for both — take your V5C, or whatever your country's equivalent registration document is, along with your own ID. Older systems are sometimes simpler, but they still need a security code tied to that specific car, obtained through the same ownership-proof route. The principle doesn't change with the age of the car: it is your car, and the process exists to confirm that.

Three practical points. Most VAG immobilisers hold only a limited number of keys, and the number varies by system, so an old key may need clearing before a new one can go in. If a key has genuinely been lost or stolen rather than broken, ask for the whole set to be re-adapted, so the missing key no longer starts the car — a key that is still learned to your immobiliser will start it, wherever it happens to be. And if you still have one working key, get a spare cut and adapted now: losing your only key is a far bigger and more expensive job than adding a second one while things are calm.

Common questions