The EHC system (rear air suspension) has multiple modes and parameters it operates within. There is a LIFT PLATFORM mode which may or may not take affect if you're only lifting the front.



The text below is an extract from the online TIS...if you want to see all of the info...click this link: https://www.newtis.info/tisv2/a/en/e...ystems/1odeF1T

The EHC control unit recognises the different operating conditions from the incoming signals and messages. Depending on operating conditions, appropriately adapted control functions are activated.

The following control functions of the single-axle electronic height control are described:

• Sleep mode
• Pre-mode (temporary start/run-on)
• Post-mode (readjustment)
• Normal operation
• Drive mode
• Cornering
• Twist
• Level-up function (only E61 All-wheel drive until 09/2006)
• Inclination detection after tyre pressure loss (only E70, E71 with 8-cylinder engine or option 4UB ”3rd row of seats”)
• Lifting platform
• Transport mode
• Production mode
  
  Transport and production modes can be set and cancelled with the BMW diagnosis system.
  If transport or production mode is set, ”power economy mode active” will be stored in the fault memory.

Sleep mode
No regulation is performed in sleep mode. Control functions that were started in other control modes are cancelled when sleep mode is activated.



Pre-mode
In pre-mode (temporary start/run-on), changes in load are equalised even as the vehicle occupants are getting in and then again for a certain time (approx. 20 minutes) after the vehicle is shut down.

In pre-mode, the ride height is only regulated to the specified height if it differs significantly from this height. The tolerance range for regulation is approx. 40 millimetres under the mean value (the tolerance range stipulates when the electronic circuitry in the EHC control unit performs regulation).

This tolerance ensures that regulation is only initiated for large loads, to increase ground clearance before pulling away. Small loads produce smaller amounts of spring travel, which are not equalised until the engine is started. These control characteristics reduce load on the battery.
In pre-mode, only the mean value of the two level sensor signals is considered.


Post-mode (readjustment)
Post-mode is used to equalise any inclination before sleep mode is initiated (fast filtering).
Control function is time-limited (approx. 1 minute).
In post-mode, regulation is restricted to a defined tolerance range (+7/-10 mm).



Normal mode
Normal mode refers to the normal operating conditions for the vehicle. Normal mode is initiated by the ”engine running” signal. Regulation is performed within a defined tolerance range on each side (±10 mm, fast filtering).


Drive mode
If a roadspeed signal greater than 1 km/h is detected, the EHC control unit will switch to drive mode.
In drive mode, regulation employs slow filtering. For example, in drive mode, changes in ride height caused by the reduction in the vehicle's weight due to fuel consumption are equalised.


Cornering
The ”cornering” control function prevents adjustments being made when cornering is detected. Slow filtering is suspended and ongoing regulation sequences suspended. Cornering is detected from an incoming transverse acceleration signal (e.g. cornering greater than 2 m/s2, less than 1.4 m/s2 when leaving bend). The DSC control unit transmits the transverse acceleration signal via the K-CAN.


Twist
”Twist” mode prevents equalisation of an inclination caused by driving over an obstacle with one wheel. Equalisation would cause a new inclination after the vehicle is driven off the obstacle, making a new regulation sequence necessary.
If the vehicle is driven onto the kerbstone and stopped, the EHC control unit will switch from drive mode to normal mode. In this control function, the signals from the left and right level sensors are evaluated.
”Twist” control function is activated if the difference in height between the left and right-hand sides exceeds a certain value (e.g. 28 mm).

In this control function, the vehicle's ride height in the middle of the axle is evaluated by the EHC control unit.
If the vehicle is loaded or unloaded, the degree of spring deflection is considered. If this value is outside the defined tolerance range (e.g. ±10 millimetres), regulation is initiated.
The left and right-hand sides of the vehicle are raised or lowered in parallel.
The difference in height between the two sides is maintained.
When the EHC control unit goes into drive mode, control function
”Twist” is terminated. An ongoing regulation sequence will be cancelled. The ”Twist” control function is ended if the height differential between the left and right sides of the vehicle drops below a predefined value.




Inclination detection after tyre pressure loss (only E70, E71 with 8-cylinder engine or option 4UB ”3rd row of seats”)
If the Run Flat Indicator (RPA) or tyre pressure control (RDC) detects a loss of pressure at one wheel, the control function will relieve the load on the affected tyre.
When the tyre pressure loss has been rectified and the Run Flat Indicator / tyre pressure control no longer indicates a pressure loss, this control function will automatically be ended after about 5 minutes with the engine running.


Lifting platform
In the ”Lifting platform” control function, any adjustment is prevented during a wheel change or other work carried out on the lifting platform.
The following conditions trigger the ”Lifting platform” control function:

• Permissible spring extension exceeded (e.g. more than 50 millimetres, recorded by left and/or right-hand level sensor)
• Vehicle raised slightly (spring extension e.g. less than 55 millimetres), regulation starts but vehicle is not lowered

The height is stored in the EHC control unit.
A reset is performed when the vehicle is again e.g. 10 millimetres under this stored height or when drive mode is detected.


Transport mode
The specified height is raised in transport mode (e.g. 30 mm). The increased ground clearance guarantees risk-free transportation of the vehicle.

Production mode
Production mode is employed for assembly on the production line and prevents regulation sequences from being initiated.
New EHC control units are delivered with production mode set. Production mode must be cancelled after the new EHC control unit has been installed.

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