Checking The Levelling System

Information 

Do not get into or out of the vehicle while adjusting the vehicle to normal level and after adjusting it to normal level (do not change the position of doors and flaps). This can give false alignment results.

Perform check under the following conditions:

• The vehicle must be standing on a level surface.
• The vehicle must be cold and must not be moved during the check.
• The room temperature should be between 10 °C and 30 °C and must not fluctuate to any great extent.

1. Only for vehicles with air suspension:  Deactivate the levelling system.
   1. 1.1 Establish operational readiness.
   2. 1.2 Deactivate the levelling system. Select CAR  > CONTROL  > Vehicle  > Chassis  > Jack mode  in the PCM.
   3. 1.3 Compress (push down) vehicle at front and rear axle twice or three times by approx. 25 mm and allow it to spring back freely.
   4. 1.4 Fit > VAS 6918 - quick clamping device  on the wheels.
      1. 1.4.1 Remove hub cap.

         > WM, 441519 REMOVING AND INSTALLING HUB CAPS

      2. 1.4.2 Mounting surfaces on wheels and adapters must be clean and flat.
      3. 1.4.3 Position quick-clamping device with the claws first in the centre of the rim and clamp it in the rim by turning the tension ring clockwise.
   5. 1.5 Determine the actual height of the vehicle body at the measuring points.

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

      Dimension X  from upper edge of measured-value pickup to lower edge of wing

      1. 1.5.1 When determining the height, measure from the lower edge of the wing to the upper edge of the measured-value pickup - dimension -X-  .
      2. 1.5.2 Add the radius of the measured-value pickup 32.5 mm  to this measured dimension -X-  .

         Sample calculation for front-axle air suspension: 

         Measured dimension X = 371.5 mm; measured-value pickup radius = 32.5 mm

         -X-  + measured-value pickup radius  = vehicle body height 

         371.5 mm + 32.5 mm = 404 mm

   6. 1.6 Measure the vehicle height (See  ) again after two hours and compare it with the first measurement.

      Dimensions and tolerances can be taken from the prescribed vehicle height for vehicles with air suspension.

      > WM, 4495TW SETTING VALUES FOR SUSPENSION ALIGNMENT

      If the vehicle is lying at an angle, there is a leak at the wheel suspension with the greatest difference between the first and second measurement.

      Spray the affected air-spring strut/air suspension bellows and the relevant air line with leak detection spray one after the other.

      If there is no difference after two hours, the vehicle height must be measured again after 24 hours.

      The following components must also be checked:

      • Air line connections
      • Air-spring strut/air suspension bellows
      • Valve unit

      If the shock absorbers are defective, oil from the shock absorber can get into the air supply system on the front axle. To ensure that the air spring system is working perfectly, it is absolutely essential that you clean the system after a fault is found or replace components.

2. Procedure for repairing the air spring system after a fault is found on the shock absorbers:
   • Replace shock absorber (complete front-axle spring strut) if there is an oil leak.
   • Screw off the affected line on the air-spring strut/air suspension bellows and solenoid valve block.
   • Clean the line several times by introducing compressed air at the end of the line at the solenoid valve block.
   • Check for traces of shock absorber oil in the solenoid valve block.
   • If the valve unit contains shock absorber oil, the valve unit must be replaced.
   • Check internal line from compressor to the solenoid valve block.
   • If there is oil in the line between the compressor and pressure accumulator, the line and pressure accumulator must be replaced.
   • If there is oil in the internal line, the compressor must be replaced.