GF32.33-P-0004RT Electronic Rear Axle Level Control, Function

GF32.33-P-0004RT Electronic rear axle level control, function
- except CODE (489) Airmatic (air suspension with level adjustment and adaptive damping system ADS)
- up to model year 08

Component Identification:

Conditions of operation
^ Ignition On or
^ Engine running

Function
The electronic rear axle level control compensates for load effects at the rear axle. To do this the system has two air spring bellows at the rear axle which take over the complete static and dynamic supporting share.

If the AIRmatic compressor unit delivers air via the electric rear axle level control valve into the left air spring bellows or right air spring bellows, then the vehicle level increases.

Conversely the vehicle level reduces if air is released via the AIRmatic pressure reduction valve (A9/1y1) in the AIRmatic compressor unit.

Depending on the load in normal driving mode the AIRmatic compressor unit operates at a pressure between 6 and 10 bar or 87 psi and 145 psi.

Wake-up input
With aid from the right front door rotary tumbler microswitch (M14/5s1), left front door rotary tumbler microswitch (M14/6s1), left rear door rotary tumbler microswitch (M14/8s1), right rear door rotary tumbler microswitch (M14/9s1), rear door locking unit and the activities of the transmitter key (A8/1) when the ignition is switched off (circuit 87 Off) the rear axle level control system control unit is "woken up" by the front SAM control unit via a hardware line in order to check the current vehicle level and to correct it if necessary.

The status of the rotary tumbler microswitch and the rear door locking unit is evaluated via the SAM control unit and reported on to the front SAM control unit via CAN-B.

When the ignition is switched on the front SAM control unit transmits a wake-up signal to the rear axle level control system control unit, as long as at least one door or the load compartment is open or an opening and closing process is in progress via the transmitter key.

As the actuation of the AIRmatic compressor unit would heavily load the on-board electrical system when the engine is not running, as a rule the AIRmatic compressor unit is not actuated in wake-up mode.

Lock position
So that when the vehicle is lifted intentionally, e.g. with a jack, air is not released continuously from the bellows, in order to lower the vehicle it is necessary to detect this reduction in load on the wheels and from it to derive a blocking position. The blocking position prevents the actuation of the electronic rear axle level control valve unit and the AIRmatic compressor unit.

If the blocking position is set by the rear axle level control system control unit, there is no display in the instrument cluster and no fault storage. The blocking position is automatically erased by the rear axle level control system control unit under certain conditions (amongst others left front axle wheel speed or right front axle wheel speed > 0 km/h or 0 mph) and the level control functions go into operation again. Output stage actuations via the diagnosis are then performed independently of the locking position status, i.e. they are always possible.