Air suspension
I have had my 2007 Mercedes-benz E320 CDI estate since new and have only recently worked out that the rear suspension is air-operated, with a 12V pump at the very front of the car and a fine bore plastic pipe to the air unit at the rear. During the cold weather earlier this year, the rear suspension failed, with a warning to stop the car. As I was within half-a-mile from home, I drove on slowly with the rear of the car sitting very low.
When I investigated the next day and started the engine, the car lifted slowly to its normal height and has been OK since. I have checked and lubricated a few things, and all seems well. Have you any idea what may have caused this? It does seem related to the low temperature of -4°C. Gareth Owen
The air compressor at the front of the vehicle draws in air via a filter, then compresses it to provide the air to support the vehicle. The air drawn in will contain a small amount of moisture and, to prevent this entering the suspension system, there is a drier and dehumidifier in the pump that should remove moisture from the air using silicate crystals. After being dried and dehumidified, the compressed air passes into the central reservoir and valve block. There is a pressure relief valve in the compressor unit used to discharge air to lower the vehicle when required. The discharged air is channelled through the air filter and back into the atmosphere. As the air is discharged it should expel any moisture and also clean the air filter.
I believe what may have happened on your Mercedes is that the air in the discharge valve, which would have contained the moisture due to be expelled into the atmosphere, has frozen in the extreme cold weather and allowed the valve to be pushed open, lowering the suspension. As no further problems have occurred since the weather has warmed up, I believe this may well have been a one-off situation and is unlikely to happen again.