Problem

• Failure of the self-levelling system
• The self-levelling system cannot be adjusted any more with the MMI
• The compressor for the self-levelling system continues to run after switching off the engine and locking the vehicle.

Technical background
Because of poor performance or failure of the compressor for air suspension the vehicle position cannot be controlled any more.

One of the following fault codes entries may be logged:
0453 - restricted function through excess temperature
1583 - leak in the system recognised
1770 - sender for compressor temperature of self-levelling control G290
1772 - signal cable of pressure sender for self-levelling control G291
2645 - valves for self-levelling control
2646 - plausibility of self-levelling control

Check with a direct current supply the compressor for the self-levelling system.

If the compressor operates with a normal working noise, check the relay J403 of the compressor for the self-levelling system.
Open the relay and assess the contacts. Compare them with the contacts of illustrations 1 to 3. Is the wear is similar or are the burn marks in the housing?
If the self-levelling compressor doesn't work or with an unusually loud noise, it is highly likely that the compressor ran permanently.
Check the contacts of the relay J403 for burn marks and wear.
A discolouring of the strand is also a clear indication for a permanent operation of the compressor,
Resolution
If the above points of 1. or 2. apply, replace the compressor and the relay J403 for self-levelling system.
If there only minor or no wear marks (see illustration 5) and the compressor has a similar working noise to a comparable vehicle, replace only the opened relay J403 for self-levelling system.