An immobiliser is an anti-theft device that is now mandatory in all vehicles. When it malfunctions, the car refuses to start and stalls almost immediately. If the immobiliser cannot detect the key, the issue may stem from a fault in the device, the key itself, or a depleted battery.
How to Identify an Immobiliser fault
Signs that the immobiliser may not be functioning properly include:
- The starter motor fails to engage.
- The engine does not ignite when the starter motor operates.
- The fuel pump does not make a sound when the ignition is turned on.
- A dashboard indicator showing a car with a key/lock lights up or blinks.
If the immobiliser cannot detect the key, experts categorise the causes into the following groups:
- Hardware issues: A faulty chip in the device or key, damaged wiring, or a drained battery.
- Software issues: Misconfigured settings, a key not paired with the immobiliser, or software glitches.
The next step is to determine why the immobiliser cannot detect the key.
Troubleshooting When the Immobiliser Fails to Detect the Key
Before assuming the immobiliser is the issue, ensure other components like the fuel pump, ignition lock contacts, and starter relay are functioning correctly. Only after ruling out these possibilities should you inspect the immobiliser.
Why Immobiliser Cannot Detect the Key
To understand why the immobiliser is not detecting the key, it is essential to know how the system works.
The process involves establishing a connection with the key, reading its unique code, and comparing it with the stored code. If the code cannot be read or does not match, the immobiliser blocks the engine from starting.
Common reasons for detection failure include weak connections, a damaged immobiliser or key chip, or insufficient electrical power. These factors are often observed if the issue occurs after an accident.
In some car models, the safety system may block the fuel pump after a collision, requiring the deactivation of this security feature.
While software-related issues that cause intermittent detection are rare, they usually result in a complete system failure. In such cases, re-pairing the key or disabling the immobiliser may resolve the issue.
Owners of cars equipped with aftermarket alarm systems with bypass modules, such as Ford, Vauxhall, Toyota, and others, often face detection problems in freezing temperatures. If the immobiliser cannot detect the key, the issue may lie within the bypass module.
Can I Start a Car If the Immobiliser Fails?
There are several ways to bypass the immobiliser when it cannot detect the key. The first step is to try using a spare original key. If unavailable or non-functional, other methods can be used.
- Using a Spare Key. If the original key is unlinked but a spare is available, try using it. This often allows the engine to start. You can then reprogram the primary key or purchase a new one and link it to the immobiliser.
Another approach involves using a bypass module key. To locate it, remove the plastic trim around the ignition lock, locate the coil, and follow its wire to a small box containing a spare key or chip that sends a signal to the immobiliser. - Using Jumpers to Bypass the Immobiliser. Some car models, such as the Vauxhall Vectra A, lack a CAN bus and use simpler immobilisers that can be bypassed more easily.
To start the car when the immobiliser cannot detect the key:
- Locate the immobiliser in the dashboard.
- Refer to its wiring diagram or dismantle the unit to identify the contacts responsible for blocking the fuel pump, starter motor, and ignition.
- Use jumpers to connect these contacts.
For modern vehicles with immobilisers integrated into the ECU firmware, this method is not applicable. Instead, consider professional car key replacement to avoid future complications.
Installing a Bypass Module
If the car cannot be started using the methods above, a bypass module can be installed. These come in two types:
- External module: A box with antennas to transmit and receive signals, often containing a spare key. It is usually installed in the dashboard.
- Emulator: A more advanced device that mimics the immobiliser’s chip. It allows the engine to start even with a non-original key, provided a high-quality alarm system is in place.
Deactivating the Immobiliser with a Code
If you have a specific code for the immobiliser, you can disable it as follows:
- Turn on the ignition.
- Press and hold the accelerator pedal for 5–10 seconds (varies by car model) until the immobiliser indicator turns off.
- Enter the first digit of the code by pressing the pedal the required number of times.
- Release and press the pedal again to enter the next digit.
- Repeat the process for all remaining digits.
- Start the car, now unlocked.
Replacing the Control Unit
If none of the methods above work and the immobiliser still cannot detect the key, replacing the control unit may be the only option. This could involve replacing the immobiliser, the ECU, or both. Some vehicles support firmware that disables the immobiliser, allowing the engine to start without its verification. However, this reduces security and should only be done if a reliable alarm system is installed.
Reprogramming Car Keys After Immobiliser Issues
If a key becomes unpaired from the immobiliser, it can be reprogrammed using a master key with a red tag.
- Sit in the car with all doors closed.
- Turn on the ignition using the master key.
- Turn off the ignition after 10 seconds (all dashboard lights should remain on).
- Remove the programmed key after a double beep.
- Repeat for all other keys.
- Insert the master key again to complete the process (you should hear three beeps, followed by two).
Most cars allow reprogramming of all keys in one session, unpairing old ones in the process. Ensure all keys are prepared before starting.
Tips to Prevent Car Key Immobiliser Issues
- Avoid disassembling the immobiliser, key, or ECU.
- Do not drop or expose keys to water or electromagnetic fields.
- Use high-quality bypass modules with aftermarket alarm systems.
- When buying a second-hand car, request all keys, the immobiliser code, and details about the alarm system.
If a used car comes with only one key, pairing new chips may not be possible without replacing the immobiliser or ECU, which can be costly.
Disclaimer: The methods described in this article are for informational purposes only. The authors and the Company (Phoenix Car Keys ltd.) are not responsible for any damage resulting from their application.
The outcome depends on the user’s skills, the type of key, and the make and model of the vehicle.
