37 00.. Notes in the event of vehicle inclination

System-specific causes (no faults) 

• The control has various modes. Different control limits apply in the different modes. The following modes can be applied when the vehicle is at a standstill on a level surface:
  • Terminal R/terminal 15 on or flap change (open door) => pre  -mode: Vehicle is not raised until mean value HA < -59 mm; vehicle is lowered at > 9 mm RL or RR and mean value HA > 0 mm
  • Engine running, vveh =0 km/h => normal  mode: Vehicle is raised < -9 mm RL or RR; vehicle is lowered > 9 mm RL or RR; (remark.: If the vehicle was moved, a control procedure is blocked until the next flap change when the vehicle subsequently stops).
  • Engine was running, vehicle is stationary, engine is off, after a counter expires => post  -mode: Vehicle is raised < -59 mm RL or RR; vehicle is lowered > 6 mm RL or RR
  • After the pre- or post-counter expires => sleep  mode: no control
• Due to the control limits, small inclinations are not corrected. e. g. a maximum inclination (RL to RR) of up to 18 mm is theoretically possible in normal mode.
• Vehicle inclination can only be checked on absolutely level and horizontal ground. For example, if the one wheel of the vehicle is on the curb, the resulting inclination is not corrected.
• Active wheel relief mode: To relieve a depressurized tire on the rear axle, the vehicle is inclined using the air suspension. The vehicle is inclined beginning at "Engine running". 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 and the engine is running.

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: see REPLACING REAR RIDE HEIGHT SENSOR  or REPLACING FRONT RIDE-HEIGHT SENSOR .
• 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 "Leakage 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 (± 3°C) 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.