This week we are troubleshooting a Mercedes-Benz S-Class that lowers itself when parked. Mercedes-Benz lowering is intermittent. In some cases, the car will drop itself overnight but not always. If the vehicle is parked on an incline or downhill the raising or lowering when parked may stop. There are many possible causes for this malfunction. Mercedes-Benz with airmatic suspension tries to self-level when parked but they end up completely lowering to the ground. In our case, the S-Class would raise to normal height when the car started. The airmatic suspension would normally work for the rest of the trip.
When one level sensor is malfunctioning, or the rod is bent, the vehicle may try to level itself unsuccessfully. This may cause your Mercedes-Benz to self-level too high or too low.
Mercedes-Benz E, C, CLK, GL, S-Class may develop any of the following issues.
- Hissss… air released by the air compressor release valve.
- You hear air compressor engaging when parked.
- Air compressor releases air when parked.
- Car lowers overnight, not always.
- Mercedes lowers drops on rear or front.
- Or Mercedes raises itself when parked
When the car is parked the airmatic will try to level the car. It does this by discharging air from the airmatic suspension strut that is too high. Typically the car is leveled by lowering the one or two corners of the car that are too high. We also have seen cases when an incorrect installation of the level sensor caused the airmatic trying to level the car by increasing air pressure at certain strut, therefore, raising the car to the maximum setting.
The cause of this problem is usually one of the level sensors. Each of these sensors has two hall effect sensors inside.
- B22/8 Left Front Level Sensor
- B22/9 Right Front Level Sensor
- B22/3 Rear Axle Level Sensor
The two front level sensors are located at the air suspension struts. In some models, you will only find one sensor at the rear axle. In this case, it measures the position of the torsion bar which provides an average vehicle height for both rear wheels.
The level sensors measure the current height of the vehicle, and those reading are stored on the airmatic control unit.
You Mercedes-Benz airmatic control unit will calibrate vehicle height. It does this so that the one corner of the car is not sitting too low or too high compared to the rest of the car.
When the level sensors are damaged they can throw off the calibration procedure. The vehicle can’t level itself, and it continues releasing air from via the pressure release valve. Eventually, your Mercedes-Benz lowers to the ground or it can also raise to the maximum setting.
It is possible for a mechanic to misdiagnose vehicle lowering as a leaking air suspension strut or leaking air hoses. This is not always the case. When ONE air suspension (airbag) strut leaks your Mercedes-Benz will drop significantly on the corner with the leaking air suspension strut.
At the air strut, there are also accelerometers whose main purpose is to determine road conditions. If the strut is moving up and down too frequently during driving the airmatic may raise the vehicle as it things that the road conditions are rough. When the accelerometer fail they generate fault codes C1123 or C1121. They also can cause the vehicle to raise to the highest setting when they malfunction.
To fix issues such as Mercedes-Benz raises or lowers when parked you need to start by inspecting the level sensors.
- Inspect the front level sensors to make sure there is no bending of the arm. Make sure the wires are not damaged. If you performed any suspension repair ensure that the level sensor at the front airmatic strut is not installed backward.
- Inspect the level sensor at the rear torsion bar. Ensure the connecting rod is not bent.
If the sensors do not have any visible physical damage, your next step is to carry a vehicle level calibration. This can be performed by an auto repair shop, or you can perform it yourself if you have a scanner capable of performing airmatic troubleshooting. You will need a scanner that provides similar capabilities to Mercedes Star Diagnostic and allows you to scan multiple control systems in your Mercedes-Benz including programming, actuating and calibrating sensors.
Watch the following video on how to access the airmatic control unit and perform calibration using the Autel DS708 diagnostic scanner.