4.8 Air Suspension issues, EHC 74 code and compressor won't switch on

[Leicesterboy15]

Hi All, I really need some help with my suspension, I've read loads of threads on this but I can't find a solution. The car is now slammed to the ground and running on the bump stops, I stopped using it as soon as this happened.

I have pulled the codes using INPA and DIS and I get the 74EHC Accumulator Pressure Remains Constant (accumulator filling requested).

When I searched for this I found that the compressor might need a rebuild so I rebuilt it with the kit and no difference. I could hear the top black part of the compressor clicking like it is trying to switch on but it then immediately throws the error again.

So I replaced the compressor with a new (aftermarket) unit and I am getting exactly the same thing. When I try to raise the car with INPA I can hear the top of the compressor clicking but the compressor doesn't kick in, when I try to lower the car I can hear a click from the rear of the car so it appears as though the signal is being sent but the compressor won't turn on. The first few times I could hear the compressor releasing air until now the pressure reads 0.5 and there is nothing left to release. The car was already slammed before this.

There is a back story:

I got the inactive warning on the dash and stupidly left it for a while, then I replaced one sensor and it turned out not to be the problem but I found that the rear sensor was seized, I bought a replacement and the found the bolt pattern was different when I went to fit the new one so I drove it for a week without the sensor, the suspension was fine.

I managed to fudge the bolt pattern and assumed the sensor was the same as the loom was identical, this new sensor didn't change anything. So I bought a genuine sensor from BMW and fitted that. I was still getting an error but the rocker light was now illuminated and I could raise and lower the car with INPA (I had always been able to do this).

Then one day as my wife was driving the car it slammed to the ground in one journey on all 4 corners at the same time which is when I stopped using it, this was about a week or so after the sensor was changed.

Since then I have been chasing the problem as above and now don't know where to look, I am not convinced that a BMW garage will know without replacing a load of parts. Oh and there is an LPG tank in the way so I can't easily get to the battery compartment.

The 2 air suspension fuses in the right rear are not connected to anything (I have 2 axle EHC) and I have checked the fuse in the glove box which is fine.

I am not sure where to go with this now, I would gladly take it to a garage and sink some money but it has to be within reason and I don't know where I am going to find the expertise in SW London. Is there anywhere else I can look? Should I get the LPG tank removed temporarily to get access to the battery compartment and the control module? Could it be that? Can this be repaired or only replaced by BMW?

I can see all the air lines and the loom disappear under the right boot cover, is there something under there that could have gone? I notice that the connectors to the top of the compressor (3 of them) are not connected to the power loom to the bottom of the compressor so I am guessing the top bit sends a reading somewhere which then sends power to the bottom part to switch on?

I am at a real loss here and I can't use the car until the is sorted, I am not sure where to go next!