BMW 7 Series: Notes In The Event Of Vehicle Inclination

System-related causes (no faults)

• Control tolerance when "Ignition off", but vehicle is awake (e. g. hazard warning switch is lit): +- 7 mm (applies from integration level 10-06-500 or CAF 4.5.4-> Read out SVK; earlier versions +- 15 mm) relative to nominal ride-level height (attention: at the front axle, the control variable is the mean value of the right and left ride height).
• Control tolerance when "Ignition on": +/- 7 mm relative to nominal ride-level height (attention: at the front axle, the mean value of the right and left ride height applies).
• When the doors are open, an automatic level correction does not take place (an active control procedure is aborted). Level changes are performed via buttons even if the doors are open
• If a strong external force acts on the vehicle during a control procedure (rapid loading and unloading), the control procedure may be interrupted; it is resumed either when driving (>30 km/h) or by pressing the ride height selection switch (down->up)
• Vehicle inclination can only be checked on level and horizontal ground. For technical reasons, it is not possible to adjust all wheel stations to the nominal ride-level height on uneven ground. For example, if the one wheel of the vehicle is on the curb, the resulting inclination is not corrected.

  The self-levelling suspension behaves like a standard steel suspension in this case.

• Active wheel relief mode: To relieve a depressurized tire, the vehicle is inclined using the air suspension. The vehicle is inclined beginning at "Ignition on". This mode is linked to the type pressure monitor and is not closed until the tire pressure monitor ceases to sense a tire pressure loss

The air in the spring struts is warmed by the engine heat and damper work and expands. This raises the vehicle.

During a journey, ride height changes due to temperature changes in the air suspension struts are corrected.

When the vehicle is stationary and switched off, these temperature effects may lead to ride height changes and inclinations that are not (cannot) be corrected. When the engine is hot, an after-heating effect that occurs after the vehicle is parked, especially at the consumer shutdown, causes the vehicle to be raised slightly and then, in the cooling-down period, to be lowered again. In extreme cases, the vehicle can be lowered by up to 50 mm at the front axle due to this temperature effect. After the vehicle is parked, the self-levelling suspension performs three control procedures in the first 48 h in which, depending on system availability, an attempt is made to reduce inclinations by raising or lower the vehicle to a horizontal level. The self-levelling suspension may lower the vehicle by up to 40 mm below the normal level. For technical reasons, inclinations in vehicles that have been parked for lengthy periods cannot be avoided in air suspension systems. Workshops are not able to check the control functions in parked vehicles due to the system complexity.

Checking the ride height adjustment

• Adjust the vehicle to the normal level
• Read out the ride heights FL, FR, RL, RR via the diagnosis system
• Measure the ride height of the vehicle
• Compare the measured ride height with the nominal value
• Ride height = measured value - nominal value
• If the deviation from the nominal value >3 mm, perform the ride height adjustment with the aid of the diagnosis system

Possible causes of mechanical faults

• Sensor linkage reversed (sensor arms must always face outward, rear axle: connector faces inward). Refer to repair instructions
• Sensor bracket twisted (holder in centering bore? Holder must be flush with rear axle support or spring bracket)
• Sensor linkage torn or bent
• Leakage (see check below)

Possible causes of electrical faults

• Water in the connector (corroded contacts) -> exchange the sensor and connector. Sensor signal is corrupted by voltage drop. Gradual process
• Short circuit (detected by control unit and output as fault message)

Leakage check

Larger leaks can be found using the following procedure. Smaller leaks are considerably more difficult to find if the effects of temperature change and axle strain are to be ruled out. Specifications stipulate that the leak may equal up to 2 mm per day (constant temperature, vehicle standing on skid pads -> no axle strain).

• Position the vehicle in a room with largely constant temperature (+- 3ºC) for approx. 10 -12 h and adjust to the normal level. Do NOT set the parking brake!
• If the vehicle ride-level height deviates from the nominal ride-level height by more than +- 10 mm, adjust the vehicle to the nominal level again (ignition on, door open - --> all doors closed, adjust level, ignition off; let the engine run in emergencies only and only for a very brief time. Do not get into the vehicle.)
• Place the EHC control unit into production mode via the diagnosis and information system (deactivated level controller)
• Measure and note down the ride heights
• Leave the vehicle standing for another 10 -12 h (constant temperature, do not move the vehicle, do not get in or out or make any other load changes)
• Measure and note down the ride heights
• If the ride heights are lower than the initial measurement by more than 10 mm at one or more wheel stations, it can be concluded that there is a leak. Leaks may occur at the air lines, the pneumatic connecting elements and the spring strut.
• After completion of the leakage test, deactivate production mode again.

NOTES ON AIR SPRING SYSTEM

Components/pipes

IMPORTANT: Maintain the highest possible standards of cleanliness around the pipe connections when dismantling and assembling components/pipes. Even the tiniest dirt particles on the pipe connections or damage to the pipes can result in leaks in the air spring system! Do not kink, twist or crush lines.

Pipe connections must be sealed off with adhesive tape immediately after they have been removed. The adhesive tape may only be removed shortly before the connection is reinstalled.

Check air spring strut/air spring for damage.

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