GF32.33-D-0005H Electronic Level Control (ELC (ENR)) Function
GF32.33-D-0005H Electronic Level Control (ELC [ENR]) Function
- with CODE (CE2) Rear air suspension
Function requirements
^ Circuit 30
^ Circuit 15 ON
^ Model 639: Status "circuit 15 OFF" and liftgate opened to t = 50 s, then the Controller Area Network bus class B (interior) (CAN-B) switches to its quiescent state (sleep mode)
^ No overvoltage or undervoltage
Overvoltage present when the voltage is > 16.2 V.
Undervoltage is present when voltage is < 9 V.
Model 639
The ELC control unit (N51/3) (and also the CAN-B) at status "circuit 15 OFF" and opened liftgate remains active for t = 50 s.
If the liftgate is closed, the electronic level control (ELC [ENR]) system and the CAN-B switch to the quiescent Circuit 30 state as quickly as possible.
The background to this is that the raise or lower level control switch (S77) is not wake-up capable, i.e. the raise or lower level control switch cannot activate the electronic level control system when it is in the sleep mode.
Model 906
The raise/lower electronic level control switch (S77/2) is not connected to a wake-up capable input of the ELC control unit (N97). Therefore the electronic level control system and the CAN-B always enters the sleep mode as soon as possible after a "circuit 15 OFF" status, because it can be activated at any given time again.
General
The electronic level control system realizes the load and mainly driving-situation specific stabilization of the rear axle level.
This provides the following advantages:
- Improvement in driving safety
- Improvement in ride comfort
- Easier vehicle loading and unloading
Operating instruction
The lock electronic level control switch (S77/1) and raise/lower electronic level control switch (with model 639 raise or lower level control switch) can be used to set the 3 operating modes for the electronic level control system:
- Automatic mode (automatic level adaptation):
- In this mode, the rear axle level is adjusted automatically while the vehicle is in motion or stationary. In this mode, the ELC [ENR] warning lamp (A1e5) in the instrument cluster (A1) and the indicator lamp in the lock electronic level control switch are not activated.
- Manual mode (manual raise and lower):
- In this mode, when the raise/lower electronic level control switch is activated (with model 639 raise or lower level control switch) the rear axle level is manually raised or lowered in each case by up to approx. 60 mm. The mode is indicated by the electronic level control warning lamp in the instrument cluster flashing on and off.
The mode is also indicated on model 639 by the indicator lamp in the lock level control switch (S77/1) flashing on and off.
- Passive/service mode (e.g. workshop):
- In this mode, no level control takes place at the rear axle, e.g. when performing work on the vehicle at the workshop or if the ELC system has malfunctioned. The mode is indicated by the ELC warning lamp in the instrument cluster and the indicator lamp in the lock electronic level control switch lighting permanently.
The electronic level control system is made up of the following subfunctions:
^ Automatic level adaptation
^ Manual raising and lowering
^ Function sequence for raising and lowering (level adaptation)
^ Manual deactivation of electronic level control system
^ Automatic deactivation of electronic level control system
Additional subfunctions for the electronic level control system are described in the following separate documents:
^ Control during vehicle standstill
^ Control when driving
^ Manual height adaptation
^ Special tasks (e.g. curb recognition, control suspension when foot brake engaged etc.)
Automatic level adaptation
The ELC control unit receives signals from the left rear level sensor (B22/7) and right rear level sensor (B22/10) as well as the following messages over CAN-B:
- Vehicle speed
- Steering angle
- On-board voltage (battery voltage (G1))
- Circuit status (e.g. circuit 15)
- Vehicle variant
Manual raising and lowering
The ELC control unit receives signals from the following components:
- Raise/lower electronic level control switch (with model 639 raise or lower level control switch)
- Lock electronic level control switch
- Left and right rear level sensors
The ELC control unit continues to receive the messages listed in "automatic level adaptation" over CAN-B.
Function sequence for raising and lowering (level adaptation)
The ELC control unit evaluates the input signals (automatic level adaptation or manual raising and lowering) then actuates the following components:
- Level control compressor (A9/1) with integrated air compressor motor (A9/1m1) and air compressor pressure relief valve (A9/11)
- Level control valve unit (Y36) with both integrated left rear level control valves (Y36y1) and right rear level control valve (Y36y2)
- Electronic level control warning lamp in instrument cluster and indicator lamp in lock electronic level control switch
The ELC control unit actuates the level control compressor with integrated air compressor motor and air compressor pressure relief valve to match the operating mode and level states of the left and right rear level sensors.
The two left and right rear level control valves integrated in the level control valve unit enable the air pressure in each of the air spring bellows to be controlled, the level for the vehicle's rear axle is then raised or lowered accordingly.
In the event of a height warning, the vehicle's rear axle level is outside the upper permissible level (at approx. +40 mm) or outside the lower permissible level (at approx. -35 mm). In this case, only the ELC [ENR] warning lamp is activated (rapid flashing) in the instrument cluster.
If the vehicle is loaded unequally there may be pressure differences in the air spring bellows. Simultaneous opening of the left and right rear level control valves, which are integrated in the level control valve unit, would cause immediate pressure compensation between the air spring bellows.
This means that the heavier side would sag, resulting in unnecessary inflation. As a consequence, the left and right rear level control valves are actuated separately.
If the vehicle's rear axle level drops below a specific value, the vehicle will then touch down on the additional rubber spring integrated into each air spring bellows. This then restricts the suspension comfort.
Manual deactivation of electronic level control system
An automatic level adaptation of the electronic level control system can be deactivated by actuating the lock electronic level control switch, this may be necessary, e.g. when changing a wheel or when performing repair work on the vehicle lift.
Finally, the lock electronic level control switch can be used to activate the electronic level control (ELC [ENR]) system and therefore the automatic level adaptation again.
Automatic deactivation of electronic level control system
Automatic deactivation of the electronic level control system takes place under the following conditions:
- When a fault was detected
- "Circuit 61 OFF" and weak battery
- In order to protect the level control compressor against overheating as a result of repeated raising or lowering of the vehicle rear axle
- When the vehicle rear axle is raised or lowered on one or both sides quickly enough
- When the vehicle stops for t = 80 s on a vehicle lift (lowering time-out period)
- When CAN-B is in the quiescent state (sleep mode)
