Common Problems With the W221 Oil Abc Strut Control Module

Common Problems With the W221 Oil Abc Strut Control Module

The W221 ABC struts have a spring and a shock absorber, just like standard struts do.w221 oil abc strut The ABC system adds a control valve(B40/1), a piston stroke sensor(B36/1), a temperature sensor(52a) and an accumulator(4 or 14). These sensors report to the control module how much fluid is in each strut. The control module then uses this information with the ride height sensors in each wheel well and inertial sensors to decide how much fluid to add to each strut to maintain the correct ride height.

The control module also has two smaller accumulators(4 or 14) that provide pressure for filling the struts with fluid during normal operation. These accumulators can fail and this will cause momentary drops in system pressure. When this happens the control module will put a "Drive Carefully" message on the dash and may also have frequent "Too Low" error messages since it cannot supply fluid to the struts fast enough to meet demand.

These accumulators can be tested by finding a small hill or speed bump that will generate a large demand for fluid from all four struts at once. If the "Drive Carefully" message comes on and the accumulator drops quickly you have a blown accumulator. You can bleed air out of the accumulator by either lifting the car or jacking it up, then opening a bleed valve in each front and rear wheel well.

Another common problem with the w221 oil abc strut is a failure of one of the 4 main control valves(B40/1, B40/2, and B36/1). These valves are used by the control module to open or close the accumulator's piston stroke sensor. When they fail the strut will have a larger stroke and be less responsive to road conditions. This can create a very bouncy ride that some people describe as a tuna boat ride.

Inside each strut there is also a travel sensor that tells the control module how far the strut has moved up or down. This sensor can fail and this will also cause a bouncy ride since the control module won't be able to adjust the strut heights correctly.

The struts themselves can also become worn out and develop leaks, but these can often be repaired by simply replacing the seals. Most repair shops will recommend a full strut replacement, but this is expensive and you will need a scan tool capable of accessing the ABC control module to get the codes and run diagnostics. It is also necessary to use SDS (or a similar scan tool that can access the ABC control module) to recalibrate the ride height settings after the replacement struts are installed. If you don't do this the ride height will be too high or too low which can damage the struts, pump, and other components over time. You can find quality struts from RMT at very reasonable prices. Their struts are made in the USA and they have a lifetime warranty against any manufacturing defects.