How to Start a Car Without a Key

How To Start A Car Without A Key And How To Prevent Car Theft

Whether you’ve lost your car keys, you happen to own a car for which you don’t have the keys anymore or you’re having ignition lock problems, you might be wondering if it’s possible to actually start a car without using the key. You might also own an expensive car and you’d like to learn ways to prevent thieves from stealing it. In all cases, this article is for you. We’ve created this quick guide explaining how to start a car without a key, quickly outlining the most common techniques used by car thieves as well as some tips and tricks to make their job a lot more difficult.


Word of warning

This article was obviously written from an auto mechanic point-of-view. We are not car thieves and we never tried hotwiring a car that we were not allowed to work on. This article was clearly not intended for this purpose. All the procedures outlined below are performed using legal equipment. And, even then, starting a car without the key is never easy. We can only assume that trying to do it, crouching under the dash in someone else’s driveway in the middle of the night while trying to avoid getting caught can only be even more complicated. We do not recommend doing that. lol

Modern Keys Do More Than Just Start the Car

Manufacturers are increasingly installing keyless ignition systems in new cars and trucks these days. Keyless ignition systems work because a module can sense the key fob when it’s close by. All the driver has to do is to press a button and the engine fires up.

However, most cars built since the mid-1990s, no matter if it’s equipped with a keyless entry system or a traditional ignition key, have some type of immobilizer installed.

With cars using keyless entry, the system is kinda simple. If the module can’t detect the key, the computer doesn’t activate the fuel and ignition systems. This will prevent the engine from starting even if the starter was powered by an outside source.

On cars using a traditional key, a transmitter is inserted in the key’s body. An immobilizer antenna is also installed around the ignition lock. If the signal is not detected when the driver inserts the key in the lock cylinder, the module will disable the same systems as on a keyless entry car.

Can A Modern Car Be Hotwired?

Older cars were reasonably easy to steal because thieves could just dismantle the ignition switch and physically turn it or rip off the wires and hotwire the car. Electrical systems were also much simpler back then. Fewer wires were running along the steering column which made it easier to identify which one did what.

Probably partly due to Hollywood movies like “Gone in 60 seconds”, many people may have the impression that hotwiring a car is easy. Movies show thieves just skinning wires, jumping them, and starting the car in an instant. In reality, hotwiring a car is much more complicated than simply touching wires together. A thief must know which wires to cut and connect without setting off alarms or disabling the car. Connecting the wrong wires or touching a ground wire with a positive wire would just make fuses and modules blow up, rendering the car inoperable.

The immobilizer problem

Also, because of the immobilizer system, car owners (and even those with some previous auto mechanic experience) will find that recent cars are nearly impossible to start when the key is lost or damaged.

Ignition systems with an immobilizer are almost impossible to hotwire. These systems are quite well-built and almost bulletproof. If you were dreaming of a special computer, as pictured below, that scans frequencies and looks for the right signal to deactivate the immobilizer system, you can stop dreaming right away. I’ve been a mechanic for over 15 years and I have never heard of such a device.

When working at a car dealer and programming new car keys for clients, a special computer and an access code to the manufacturer’s database is required. Unless you plan to land a job at a car dealer to gain access to the database and succeed in getting your hands on the right equipment, I doubt you’d be able to hotwire a car equipped with an immobilizer system.

Unfortunately, there are very few workarounds available to drivers of modern vehicles who lose their car keys. Getting a replacement key is usually the only solution.


Car thief using a computer to start a car

How Do You Hotwire a Car?


The process of starting a car without the key, also commonly called “hotwiring” is not that difficult, in principle. I say “in principle” because, in practice, it is a different kettle of fish.

The ignition switch allows or prevents the current to go from the battery to the different electrical components. Wires running from the ignition switch power the dash, lights, stereo, and the ignition system. One of the wires also runs to the ignition coil, one to the starter, and one to the battery.

In theory, all the engine really needs to run is power coming from the battery and powering the ignition, fuel, and starting systems. Once the ignition and fuel systems get the much-needed 12V and the starter starts spinning, there’s no reason for the engine not to start. Pretty much all the other systems are only related to accessories and such.

To hotwire a car, one must technically cut the wires running to the battery, starter, and ignition, twists the battery and ignition coil wires together, then strike the ignition wire against the twisted wires. The resulting transfer of energy signals the starter solenoid to engage the starter, and the engine starts. The engine would theoretically die out when the driver untwists the battery and ignition wires.


However, when it comes to practice, it’s a whole different story. What makes it really complicated to hotwire a car is the fact that the ignition switch often has many other wires routed to it. Furthermore, manufacturers do not typically follow a standard wiring color diagram, so these wires can also be different colors. It’s not like the fuel pump or ignition system wires will be labeled or anything. There’s also a ton of unrelated wires in there, powering wipers, blinkers, audio system control, etc. Unless you have access to the car’s wiring diagrams found in a repair manual, it’s unlikely you’ll be able to find the right wires.

Also, immobilizer systems often disable many other systems to make it even more difficult to hotwire a car. For example, it’s not uncommon for immobilizer systems to control things such as injectors. Other types might also control the ignition timing and the ground distribution of several components. In that case, it would mean that even if you were to power the fuel pump, the injectors would stay closed. The ignition could also be de-synchronized or the ground circuit of the fuel pump might be opened, preventing it from working.

Every immobilizer system is unique and unless you know how the system works on a specific vehicle, hotwiring it might be quite complicated. It’s not impossible but, trust me, it’s not for newbies.

Car thief hot-wiring a car ignition switch

Tricks Car Thieves Use to Start Cars Without a Key

As the technology to prevent auto theft evolves, thieves become smarter. Today, car thieves do not rely on abilities to slim-jim a door lock and hotwire a car. Instead, they use inexpensive computer devices called repeaters. Repeaters work by replicating the signal a transponder produces. I know that I’ve said that computers used to magically start cars like in the movies didn’t exist. However, repeaters are a bit different.

Indeed, the type of computers used in “Gone in 60 seconds”, capable of starting any random vehicle at the touch of a button doesn’t really exist. Repeaters, on the other hand, can’t unlock and start just any car. They also only work with keyless car entry-equipped vehicles. For this technique to work, the thief has to either follow the car owner until he records the signal or by illegally getting his hands on the keys.

The owner of the repeater must be very close to the transponder to detect and replicate the signal. Some models only work when they are in close contact with the transponder while others can record and save the signal. For this reason, car owners should be aware of talking to strangers when they are getting into their car at a gas station or a grocery store, for example. These are opportunities thieves take advantage of to copy a transponder signal, which they’ll be able to later use to start the engine and steal the vehicle.

Installing an Immobiliser Device on Older Cars

Luckily, owners of older cars can use some simple tricks to act as immobilizers. These are called kill switches. Kill switches work like immobilizers by interrupting the electrical current to the ignition coil or starter solenoid. Even better, these devices are usually simple and quite inexpensive to install.

The most common technique is to put the switch somewhere convenient, but not easily noticed. Under the dash or under the driver’s seat are good spots. Under the floor mats also work fine but try to avoid it if you live in cold climates. I’ve once been stuck for hours in a parking lot because snow had covered the switch with ice. I had to spend at least an hour heating up the ice with a lighter…

Other more complicated systems use a combination of factory-original button push-sequence to disengage the switch. Remember those “buckle the seat belt – turn the lights on – two push on the defrost” type of sequence? These are not as widely spread as they were before, mostly because they were just awful to use.

Ignition Coil Kill Switches

Another easy DIY kill switch trick is to interrupt the flow of electrical current to the positive side of the ignition coil. If the coil circuit is open, car thieves may try to hotwire the car as much as they want, it will never start.

To do that, buy a single-pole/single-throw switch. By cutting the wire running to the ignition coil and installing the switch, thieves will not be able to start the car unless they know where the switch is located or by bypassing the circuit completely. The same technique also works with the voltage regulator or starter solenoid for a similar result.

Fuel Cut-off Kill Switch

One type of kill switch that can be installed on older and newer vehicles is a fuel cut-off switch. Just as with a coil kill switch, a fuel kill switch will simply prevent hotwiring from powering the fuel pump.

There are two ways to do it. One is to install a kill switch that prevents electric fuel pumps from receiving power. Another method involves an electric switch that shuts off the flow of fuel to the engine. This type of switch works well on mechanical fuel pump-equipped cars and trucks. Without the fuel pump, the car will start and run for about 20 seconds. Once it dies, it will not restart.

Or, if you are lazy like me, you can also just take out the fuel pump relay every time you leave your car in an unsupervised parking lot. I wish the best of luck to the car thief who tries to start my car without a fuel pump relay! Locating the problem and realizing there’s a relay missing somewhere will take so much time that he’s probably better just to steal the car using a tow truck.

In Brief…

When they have lost their key, most car owners will find it is easier to get a replacement key instead. You can also try to replace the battery in the key fob first. In an emergency, it’s never a good idea to try and hotwire a car. Unless you know what you are doing and which wire does what, you will probably do more harm than good. In that case, you’re better calling for a tow truck right away. Bring your car to the nearest dealer and have a new key programmed instead.

And yes, car keys can be expensive but it’s still cheaper than having to replace a burnt PCM.


About Derek F

Derek grew up in Southern California and started working on cars when he was a child. He learned from his father and grandfather how to make basic repairs and maintain cars correctly. Derek rebuilt his first engine at 15 years-old, beginning an automotive career that took him to many interesting jobs. Derek has worked as an automotive detailer, managed parts warehouses and auto parts stores, and worked as a mechanic for several years doing brake and suspension work. While pursuing a bachelor’s degree in government journalism, Derek worked for an auto museum where he started to write about cars. Today, Derek uses his expertise gained from many years of practical experience to help educate DIYers and share interesting knowledge about various types of automotive repair and service. Writing about cars helps fund his numerous classic car restoration and customization projects.

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