Keyless Go

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:

• The central locking system
• The comfort opening / closing of the side windows and sunroof
• The alarm control system
• The tyre-pressure monitoring
• The immobiliser

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 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.

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:

• The ID transmitter is detected by the driver door or trunk.
• The vehicle is actively unlocked using the remote control.
• The vehicle is mechanically unlocked using the emergency key.
• The comfort opening function is not available with passive opening.

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:

• Position 1 = S-contact switched on (radio switches on)
• Position 2 = terminal 15 switched on
• Position 3 = The ignition starter switch / ID transmitter moves to this position automatically once the engine has been started (terminal 15 driving)
• Position 4 = Engine start (terminal 50)

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.

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.

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.

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.