Keyless Go

Here you will find useful basic information and important tips relating to Passive Entry / Go in vehicles.

Thanks to the major advances made in vehicle electronics, comfort systems in vehicles are becoming more and more common. On this page, you can find out about how the keyless entry system Keyless Go works, and the safety circuits that are intended to prevent operating errors. You will also find useful tips for troubleshooting in the event of faults relating to this comfort system.

Important safety note
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.

KEYLESS GO ENTRY SYSTEM: BASIC PRINCIPLES

With the Passive Entry / Go system, the vehicle is locked and unlocked – and the engine started and stopped – passively. With these new systems, all the vehicle's user has to do is keep the radio transmitter key with them. This saves the user from searching for the radio transmitter key and having to actively hold it and press the radio transmitter buttons in order to activate the required functions. These entry and driving authorisation systems increase user comfort and make entering the vehicle easier. The system from a Passat B6 is used as an example to describe the functions and components. The vehicle manufacturer's specifications are required in order to obtain detailed information on the specific system used in any particular vehicle.

 

In order for the Passive Entry / Go function to work, a number of system components need to be added to the conventional central locking system. These include:

Design of the ID transmitter

The ID transmitter consists of a splash-proof housing that contains the electronics, antennas, and buttons. The buttons used to actively operate the functions (e.g. unlocking, locking, trunk, panic button) are integrated into the top of the transmitter. The casing also contains a small LED indicator lamp that lights up when a button is pressed, for example. A 3D LF antenna and an LF pre-selector IC with an integrated microcontroller allow precise measurement of the received field strengths in all three spatial directions. This enables the system to differentiate precisely between the interior and exterior of the vehicle. The antenna for UHF reception is built into the PCB.

 

The ID transmitter also has a battery monitoring system. If the battery condition reaches a critical level, a warning message appears on the vehicle's display. In addition to this, the LED indicator lamp will no longer light up when a button is pressed if the battery needs to be changed. In order to conserve battery life, intelligent wake-up algorithms ensure that the ID transmitter is not "woken up" unnecessarily (e.g. by other radio transmission systems). A built-in day counter allows ID transmitters that are not in use (e.g. spare keys) to be put into "power-down mode." This maintains the battery capacity for a longer period of time.

Radio communication

In order to perform a function on the vehicle, the system checks whether the user has an authorised ID transmitter. The control unit sends a signal, which is triggered by the capacitive proximity switch on the door handle, to the ID transmitter, and receives a response on a UHF frequency (433 MHz or 315 MHz). In addition to transmitting data to the ID transmitter, the signal sent by the vehicle via the LF antennas on the 125 kHz frequency is also used to clearly locate the ID transmitter.

 

This enables the system to determine with high precision whether the transmitter is inside or outside the vehicle. This precision is required in order for the control unit to ensure whether there is an authorised ID transmitter in the vehicle interior and the start authorization can be given, or whether an ID transmitter left in the vehicle after locking needs to be deactivated (if the vehicle is locked from the outside using a second authorised ID transmitter).

KEYLESS GO FUNCTION: OPERATING PRINCIPLE

Important

If the battery in the ID transmitter runs out, it will no longer be possible to start the vehicle using the ignition starter switch. If this happens, you will need to remove the ignition starter switch and place the ID transmitter in the ignition lock instead. The ID transmitter contains a transponder pill that is powered externally, separate from the battery. This is used to deactivate the immobiliser and only works in the ignition lock, thus allowing you to start the engine in such situations.

NOTE ON ELECTRONIC STEERING LOCKS

As soon as the ID transmitter has been taken out of the ignition lock, the electronic steering lock engages. Since the ignition starter switch can be left in the ignition lock, the electronic steering lock will not engage until all authorised ID transmitters have been removed from the interior of the vehicle.

Opening and locking the trunk

The trunk can be opened and closed without unlocking the entire vehicle. If there is an authorised ID transmitter within effective range of the rear antenna, the trunk can be opened by pressing the the tailgate unlocking mechanism (pressing the VW emblem). If the trunk is closed again while the authorised ID transmitter is within reception range outside of the vehicle, the trunk is automatically locked again.

SAFETY CIRCUITS OF THE PASSIVE ENTRY GO SYSTEM: BACKGROUND INFORMATION

ID transmitter in the interior

If the ID transmitter is in the vehicle interior, it is not possible to also lock the vehicle from outside. This makes it impossible to lock the ID transmitter inside the vehicle.

ID transmitter in the trunk

It is impossible for the user to accidentally lock the authorised ID transmitter in the trunk if the vehicle doors are already locked. If the ID transmitter is detected in the trunk in such situations, the trunk immediately opens again automatically.

Deactivation of proximity sensors in the door handles

If the vehicle is parked very close to a hedge – or similar object – and locked, there is a risk of leaves/branches etc. activating the proximity sensor in the door handle. If this happens, the sensor will then try to find an authorised ID transmitter. In order to conserve battery life in such situations, the proximity sensor is deactivated for 30 minutes if abnormally frequent activations occur. If this problem occurs at the driver door, only the sensor in the driver door will be deactivated. If the rear or passenger doors are affected, these will all be deactivated together. The sensors are reactivated when the vehicle or trunk is opened using one of the sensors that is still active, or when the unlock button is pressed on the remote control.

KEYLESS GO - FAULTS AND DIAGNOSTICS: TROUBLESHOOTING

Due to the complexity of the systems used in modern vehicles, troubleshooting can be an arduous process. This applies to both the electronic and the mechanical parts of the vehicle. However, mistakes made by users when operating Passive Entry / Go systems can also lead to the impression that the systems are not working properly. As such, it is important to follow the operating instructions and the manufacturer's specifications precisely.

 

Due to the design of the system and the CAN bus networking of the control units, troubleshooting is not possible without a suitable diagnostic unit and manufacturer-specific documentation such as repair instructions, circuit diagrams, and functional descriptions. For instance, in our example vehicle, the Passat B6, three separate control units and the ignition lock all need to be enabled in order to unlock the electronic steering lock.

 

This type of redundancy is built into the system in order to meet the stringent security requirements. It is also becoming more complicated to replace defective control units. In the Passat, the control units (e.g. comfort control unit, engine control unit) that are part of the immobiliser system can now only be taught online. This means that an authorised garage always needs to be contacted, even after the diagnostics have been run successfully.

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