Keyless Go entry system
Here you will find useful basic information and important tips relating to Passive Entry / Go in vehicles.
Important safety note
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:
The Passive Entry / Go functions in the Passat B6 are operated by the body control unit for comfort systems. This "comfort control unit" is located to the right beneath the dashboard, behind the glove compartment.
The comfort control unit controls a number of functions, including:
This control unit is also responsible for monitoring errors and storing them in the system. Depending on the region, communication between the radio transmitter key and the control unit takes place in the frequency ranges 433 and 315 MHz.
The ID transmitter is a radio transmitter key with added passive functions. As such, it is a combination of a simple remote control and an identification transmitter.
In order to actively lock and unlock the vehicle from distances of up to 100 m, the button on the ID transmitter must be pressed manually. Passive unlocking is performed by gripping the door handle, while passive locking is performed by touching a sensor surface on the door handle. For security reasons, the passive functions can only be used when the ID transmitter is in the immediate vicinity of the vehicle (approx. 2 m). The ID transmitter communicates with the control unit via radio waves.
It also contains a mechanical emergency key that can be used to unlock the driver door if the battery in the radio transmitter runs out, for example.
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.
The front door handles contain the receiving antennas and the proximity and locking sensors for detecting when the vehicle should be opened or closed. The rear door handles only have sensors for detecting when the vehicle should be open or closed.
The proximity sensors work according to the principle of capacitive sensors. As soon as the driver's hand comes within range of the proximity sensor, this is detected by the capacitive sensors and transmitted to the comfort control unit in the form of a signal.
In addition to those in the door handles, there are other antennas on the outside and built into the interior of the vehicle. On the outside, these include the rear antenna, which is built into the rear bumper and responsible for reception at the rear of the vehicle.
The interior contains the antennas for the interior, trunk, and parcel shelf.
The interior, trunk and rear antennas each comprise a ferrite coil with a capacitor, and are constructed as a series resonant circuit. The parcel-shelf antenna is a flexible PCB with a conductive loop that acts as the field generator.
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).
When a vehicle user with an authorised ID transmitter approaches the vehicle and comes within the receiving range of the proximity sensors, the system "wakes up." The radio transmission connection is established via the ID transmitter and the antennas in the door handles. The system checks whether the ID transmitter is authorised for this vehicle by checking the validity of an internal electronic/logic "key." If the control unit recognises the ID transmitter as being authorised, the central locking system is activated and the vehicle is unlocked. Depending on the encoding – individual or all-door locking – the doors can then be opened. The whole procedure, from the activation of the capacitive sensors in the door handle to the unlocking of the vehicle, takes approx. 50 – 60 ms.
If the vehicle is not used for a longer period of time, e.g. during a vacation, the proximity sensors in the passenger door and the rear door are deactivated in order to optimise current consumption.
In order for the sensors to be reactivated, one of the following events must occur:
There are two ways of starting the engine on this vehicle: With the ID transmitter or the ignition starter switch (start button). The Passat has an ignition lock that both the ID transmitter and the ignition starter switch can be inserted into. This offers the same functions as a standard ignition lock. When using an ignition starter switch, this can be left in the ignition lock. All that then needs to happen in order for the engine to start is for an authorised ID transmitter to be detected inside the vehicle. This form of ignition lock differs from a standard ignition lock in that there is no need to turn the key – the ID transmitter or ignition starter switch is simply pushed into the ignition lock.
The device in the lock can be pushed into the following positions:
In order to start the engine, the ignition starter switch / ID transmitter is pushed in up to position 4. As soon as the engine is running, the ignition starter switch / ID transmitter is simply released.
In vehicles with a manual transmission, the engine can only be started if the clutch pedal is pressed. In vehicles with an automatic transmission, the brake pedal must be pressed. In vehicles with a diesel engine, the preheating function works in much the same way as with a conventional ignition lock. After turning on the ignition, wait until the preheater light goes out before starting the engine. Do not push the ignition starter switch / ID transmitter into the "engine start position" until this has happened.
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.
To switch off the engine, the ignition starter switch / ID transmitter must be pressed all the way into the ignition lock again. When it is released, it automatically jumps to the "ignition on" position. Pull it out to the next position in order to switch off the ignition. Another difference between the ID transmitter and the ignition starter switch is that the ID transmitter can simply be pulled out of the ignition lock, while the ignition starter switch is locked in and can only be removed after unlocking. To unlock the ignition starter switch, pull it out of the ignition lock up to the limit stop. Press the unlock switch on the underside of the ignition starter switch, then pull it out.
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.
Like unlocking, locking can be performed either actively using the remote control or passively by touching the locking sensor in the door handle. However, there must be an authorised ID transmitter outside and close to the vehicle for this to work. If the locking sensor is touched once, the vehicle is locked and the "safe function" is activated. If the locking sensor is touched twice, the vehicle is locked, but the "safe function" is not activated. "Comfort locking" can also be performed using the passive locking system. In order to do this, the locking sensor must be touched for longer than two seconds. The system also has a security lock. This means that the vehicle locks again automatically if a door or tailgate is not opened within 30 seconds of the vehicle being unlocked.
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.
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.
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.
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.
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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