Discover how your vehicle’s engine immobiliser works, how to deal with common faults, and what other measures you can use to keep your vehicle safe.
What is an engine immobiliser?
As the name implies, an immobiliser prevents a vehicle from starting unless the correct key is inserted into the ignition. Since 1998 all new cars in the UK have been fitted with an immobiliser, resulting in a dramatic drop in car thefts.
An immobiliser system comprises a key fob containing a special electronic chip. When the vehicle's electronic control unit (ECU) or immobiliser control unit (ICU) detects this chip (via a transponder inside the ignition barrel) it allows the ignition to be switched on and for the vehicle to be driven.
Some older immobiliser systems featured a fob separate to the key, or would only work when a button was pressed inside the vehicle, which would deactivate the system.
Other early systems featured a keypad which would deactivate the immobiliser when the correct four-digit code was entered.
Keyless and app-based entry
Some modern systems deactivate the immobiliser when the key fob is in the vicinity of the vehicle, while others allow owners to use a phone app to do the same.
Older systems used a single code to gain entry, while newer ones use a different code each time the fob is used - thereby enhancing security.
How does an immobiliser work?
By controlling the operation of the starter motor, fuel system and ignition system, your vehicle's immobiliser prevents theft. This means that even when the right key is used, unless the transponder receives the correct code, the vehicle will not be drivable.
What about 'hot wiring'?
'Hot wiring' is the process of bypassing a vehicle’s immobiliser. But while this practice was once more common - and featured in countless films and TV shows - modern systems will not permit the starter motor and/or fuel system from responding unless the right code is received.
Does my car have an engine immobiliser?
If your car was bought new in the UK anytime since 1998, it will have an immobiliser.
This legal requirement has seen vehicle theft plummet by 40 per cent - according to some studies.
Some luxury cars built between 1992 and 1998 also featured engine immobilisers, with transponder-embedded keys. BMW even had a keypad entry immobiliser installed in some models before 1992. However, this was quite basic technology compared to what would follow.
Not sure if your car has an immobiliser? Check your user’s manual or get in touch with the manufacturer. Some older vehicles may have had an 'aftermarket' immobiliser system fitted later on.
How to fix an engine immobiliser?
Modern immobilisers tend to work well for the lifespan of the vehicle, but malfunctions do occur. These issues can mean that a vehicle won't lock or unlock, or the engine won't start. Errors can also cause the alarm to go off.
If your immobiliser develops a fault, read your owner’s manual in the first instance; it may explain how to fix your engine immobiliser, particularly if it's a simple issue like a flat fob battery (see below).
If this doesn't provide a solution, you may then need to contact your dealership or a trusted mechanic to help remedy the issue.
A flat key fob battery: the most common issue
A dead or dying key fob battery can cause immobilisers to stop working properly. Thankfully, this is a very easy problem to resolve - and one that you can manage by yourself. A new battery should only cost a few pounds, depending on the make and model.
However, if replacing the battery doesn't work, there could be an issue with the wiring or electronics of the fob or other part of the immobiliser system.
The different immobiliser types: explained
Modern cars have immobilisers fitted in the factory, and should function as required time after time.
Some feature undetectable installation, WiFi connectivity and dashboard-based pin code entry, among other features.
Some older systems have been found to be vulnerable to hacking.
Note that if you do have an older vehicle without an immobiliser you can have an after-market immobiliser installed. This is likely to reduce your car insurance premium.
The various anti-theft devices have been graded by Thatcham Research, a road safety organisation that evaluates both electronic and physical theft prevention systems in a completely unbiased way.
It's highly recommended that you only purchase anti-theft devices that have been tested and verified by Thatcham.
Here are the seven Thatcham Research categories:
Category 1 – Electronic Alarm and Immobiliser
Vehicles in this category must have an alarm system with perimeter detection and sensors capable of identifying vehicle movement.
The immobiliser must control at least two of the vehicle's operating systems.
Category 2 – Electronic Immobiliser
This category applies to vehicles equipped with electronic immobilisers.
These systems must control a minimum of two critical vehicle functions.
Category 2/1 – Electronic Alarm Upgrade
This category covers vehicles that have had an aftermarket alarm system installed when previously no factory-fitted alarm was present.
Upgrading to this system improves security and may help reduce insurance premiums.
The alarm must meet the same standards as Category 1 systems.
Category 3 – Mechanical Immobiliser
Vehicles in this category are equipped with mechanical devices, such as steering wheel locks or wheel clamps. These devices must be manually applied each time the vehicle is left unattended.
Category 4 – Wheel Locks
This category includes wheel locking devices, such as locking wheel nuts, which require a unique tool for removal. These devices act as both a theft deterrent and a visual security measure.
Category S5 – Post-Theft Tracking
Systems in this category are designed to track a vehicle's location if it is stolen. They include features such as remote immobilisation, police or security alerts, and driver identification, typically through a small tag without which the vehicle cannot start.
Category S7 – Stolen Vehicle Location
This category covers systems specifically designed to locate stolen vehicles.
Is it worth getting an immobiliser fitted in an older car?
Various studies have looked at the impact of immobilisers, with some suggesting that they have helped reduce car theft by 40%. With this in mind, it's undeniably a smart move to have such a system fitted if you have an older vehicle.
It’s also very likely to bring down your insurance premium, since not having one fitted probably meant you were paying more due to the risk of theft being perceived as higher.
Installation can cost up to £500, depending on the system and labour required. Many firms will come to your location to fit the immobiliser.
Do engine immobilisers provide 100% protection?
While modern immobilisation technology is highly effective at preventing vehicle theft, thieves still have ways of operating.
Some of these work-arounds are rather basic - such as using a flatbed truck to carry your vehicle away. Others are more sophisticated, such as harnessing wireless relay transponders to clone key codes.
Keyless car theft, in fact, is increasing, accounting for a large number of the more than 100,000 vehicles that are stolen annually nationwide.
To combat this, some carmakers now allow keyless entry to be disabled.
Owners might also choose to store their keys in a 'Faraday bag', which blocks electronic signals, thereby preventing keyless theft.
Are there any other ways to protect my vehicle?
Yes. To give your vehicle maximum protection, you could implement a combination of electronic and physical anti-theft devices.
Electronic devices include alarms systems, remote immobilisation, vehicle trackers and driver identification.
Physical devices include steering wheel locks, wheel clamps, and gear locks. These somewhat old fashioned devices are highly effective visual deterrents, even if thieves have a flatbed lorry at their disposal.
