Suspension Control ( Automatic - Electronic ): Description and Operation

Four-wheel self leveling suspension system, function
Via a pneumatic suspension system on the rear axle, the four-wheel self leveling suspension system compensates for differing loads and keeps the vehicle level at a constant target position (boot loading).
For this purpose, the distance between the rear axle and the bodywork is determined by means of a self leveling suspension system sender. In case of a deviation from the target position, the volume of air in the suspension is varied by means of a compressor and solenoid valves in such a way that the target position is restored.
The system features a lifting-platform detection system.
Height adjustment and charging of the system is necessary after repairs, replacement of the control module and/or vehicle-level sender.

Level control system control module -J197-
The control module registers all the data from the leveling-system senders and sensors and uses it to determine current vehicle position. This is then compared against the target position and corrected if necessary.
The control module performs a self-testing routine when the ignition is switched on. The control module is housed in the air-supply unit.

Level control system sensors -G76-, -G77-, -G78-, -G289-
The leveling-system senders are so-called angular resolvers. The level of the vehicle, i.e., the distance between the superstructure (bodywork) and axles is measured by means of four senders in order to determine vehicle level.
Any change in vehicle height is converted by means of a coupling mechanism into a change in angle in the sender and is transmitted to the self leveling suspension system control module.
The special feature of the Allroad Quattro is the fact that the power for the left-hand leveling system senders (G78 and G76) is supplied from control module J431 of the headlight range control system. Senders G77 and G289 on the right-hand side are supplied from the control module for the pneumatic suspension system, J197. The reason for this is that the headlight range control system remains serviceable if control module J197 fails (safety relevant).
The level sensor features two different and separate output signals (angle signals). The four-level pneumatic suspension system uses the PWM signal and the headlight range control system utilizes the angle-proportional voltage.

Suspension strut valves -N148-, -N149-, -N150-, -N151-
The suspension-strut valves (also referred to as transverse check valves) permit raising and lowering of the vehicle.
The suspension-strut valves are activated by the self leveling suspension system control module. The valves are grouped together in a solenoid valve block.
These valves take the form of 2/2 way directional valves and are of the Normally Closed (NC) type.

Level Control Accumulator Valve - N311-
This valve is used for switching-in of the pressure accumulator when the vehicle is stationary.
The pressure accumulator valve is activated by the self leveling suspension system control module.
The valve is an element in the solenoid valve block.

Solenoid for level control system -N111-
The self leveling suspension system release valve is used for lowering of the vehicle.
It is activated by the self leveling suspension system control module.
The release valve is integrated into the compressor unit and is of the Normally Closed (NC) type. It is used for pressure limitation and for setting of residual pressure.

Motor for compressor-level control system -V66-
The compressor motor drives the compressor, by means of which the vehicle can be raised via the air-springs.
The motor is activated by the control module via relay J403 for the self leveling suspension system compressor.

Relay for compressor level control system -J403-
The relay is positioned between the compressor motor and the control module for transmission of the power current.
The compressor relay is switched by means of the self leveling suspension system control module.
The relay is located at Relay Position 6 on the eight-position relay board.

Level control pump temperature sensor -G290-
The compressor temperature sender transmits to the self leveling suspension system control module a signal indicating the temperature measured on the compressor.
A temperature model that prevents overheating of the compressor is computed in the self leveling suspension system control module in conjunction with compressor operating time and the temperature signal.
The compressor temperature sender is integrated into the compressor unit.

Level control system control head -E281-
The self leveling suspension system operating unit enables the driver to perform manual level adjustment. The various height levels (Low, Normal, High 1, High 2) can be selected by means of two buttons (High and Low). The level selected is indicated by means of LED's.
The self leveling suspension system is deactivated if both buttons are kept simultaneously pressed for a minimum of 5 seconds.
The operating unit is located in the center console.