Folks

I write this purely in the hope that it will help others. I have spent way too much time, money & tears trying to fix my "Self Leveling Suspension Inactive" issue on my e53 4.8is. Being a 4.8is it has the EHCII or Twin Axle air suspension.

Things to keep in mind when trying to diagnose and fix your suspension once it starts displaying the message "Self Leveling Suspension Inactive"

This message will 'normally' remove all power to the actual compressor ensuring that it will not operate by using the ride height button. This is important to understand as I see many in the forums who spend time and money trying to get power to the compressor, replacing fuses, relays and even the compressor.

This is a "safety" feature, to protect you and the car. The easy way to test this is to use a diagnostic scanner that can read EHC errors and clear them! Once the error is cleared the suspension will start to operate until the error returns, which could be seconds, days, weeks or even months.

With the error cleared you should now be able to start diagnosing.

There are five probable areas that can cause the system to fail. Spending time looking at these will help you and save you money. A good Scanner/Diagnostic Tool is really a must but not always an essential.

1) Air Bags: One in each corner. If they leak? The car will sag in that corner(s) This may take time to become visible. Park the car on level ground and leave as long as you can (the longer the better) if it sags in one corner? You have a leak in that corner and need to replace the bag.


2) Compressor: These units get tired as they age. They are designed to keep the reservoir topped up by running briefly for a few seconds in any one time. They are not designed to for long runs. If you have a leak. The compressor attempts to keep the system inflated and burns out. Fixing the leak is crucial. Then buy a rebuild kit from www.bagpipingandy.com The kit costs a fraction of the price of a new compressor and is relatively easy to install using a 1/4 drive socket set, screwdriver and some torx bits. Rebuild time around 1 hour. The kit consists of a new piston ring, seals, bolts etc and (best of all) colour, detailed instructions. You can also buy a new cylinder bore and drier refurb kit if you want to rebuild the whole unit (I did) and it is worth every penny. This way you are only doing the job once.


3) ECU: For this you really do need a good scanner that will interrogate the ECU in depth. These rarely fail and are very expensive to replace. If your compressor is lifting and lowering the car, it is unlikely that the ECU is at fault.


4) Reservoir/Connectors: These do fail. A spray with diluted washing up liquid should show any bubbles as leaks. It is not unheard of to damage the connectors by removing the spare wheel. These are all speedfit connections and easily replaced.

5) Ride Height Sensors: These are known to fail and relatively cheap to replace
They can be read using inpa or a good scanner. They can also be seen to have broken, normally after the car has been lifted on a jack or ramp??


Other things to consider:

The compressor has a heat sensor that will kill the power, if it kicks in. The sensor detects heat caused by continual running. It can be seen operating using inpa or other good scanners. Remember!! If the compressor is continually running or, running for longer than a couple of minutes you most likely have a leak.


In my own mission to repair my compressor. I found that the drier was badly rusted (they will all collect moisture that is their job) but the pepper pot holes were blocked by rust restricting air flow. Some of the rust had been drawn into the cylinder bore, scoring the piston ring and bore. This allows air to escape and reduces pressure while extending running time.

All these parts were available from www.bagpipingandy.com and delivered in a couple of days along with a complete set of springs, bolts etc.

The bottom line is that the compressors get old and tired and do need a refurbish. It is a cost and time saving task that works instantly.

Lastly.

Andy (bagpingandy) has been a huge help to me as I struggled through diagnosing and repairing my system. Had I simply bought and installed his kit I would have saved weeks of pain and a large amount of cash. It is very easy to get carried away trying to fix what is staring us in the face. Andy's help, time and effort made a world of difference to me and is all encapsulated in his full colour instructions that come with each kit.

I am not associated with Andy he has not asked me to wrote this. I am an avid enthusiast who believes that good work deserves good recognition.

Have fun.

Bruce