Hi all,

I've been struggling with a battery drain issue which I think I have tracked down to my air suspension system. My relay R1 in my engine bay fuse box is constantly audibly ticking, even after replacement with a new relay. I have confirmed this drain with current draw tests with a multimeter in series, showing what I believe to be acceptable quiescent draw (c. 30 milliamps) when the R1 relay is unplugged and car is left to go to sleep (current draw test constantly in the hundreds of milliamps with R1 relay in place, draining battery in 3-4 or so days if car isn't used).

While my fault finding has led me this far, I don't have real knowledge of how the air suspension system works electronically (lack of knowledge means I'm struggling to read/understand the X350 electrical diagram), and whether there are particular components that could cause a current draw like this. If anyone has any advice or could help me, I would be really grateful!

It's important to mention that my air suspension is generally performing fine, with no major faults and no related codes on SDD - the only thing of note is the compressor can be quite noisy for 15-20 seconds within the first 2 or 3 minutes of a drive from cold start, especially noticeable in colder weather, but as I said, unsure if this is an important clue or not!

Any help is much appreciated

Thanks in advance

 

For some reason your air suspension module is trying to run your compressor even when the key is off. I believe there is one set of conditions where this can happen. It would appear that your compressor will not run on the battery voltage and needs the higher voltage from the alternator. One would think you have a bad ground for the compressor or the compressor is on the way out. Your noisy first run may be pointing to the failing compressor.

 

Thanks OldKarz, much appreciated. I will be taking a much closer look at the compressor in the next few days, and will check out the grounds definitely. I am also going to have a look into the module as well.

 

If the relay R1 is ticking, then you would expect the compressor to be getting pulsed on with each ticking cycle of the relay.
There is no feedback to the ASM about compressor operation or current draw other than whether the reservoir is reaching correct pressure (sensor in valve block).

If SDD is showing the ASM to be present on the car's network, then it is not a missing comms issue to the ASM.
The ASM should not be attempting to run the compressor once the car is switched off (to preserve battery), so it appears the ASM is malfunctioning.

Two things to try.........

• Check the ASM earth (G17 - rear cabin RHS below rear seat)
• Try a hard reset of car (disconnect battery) to force all modules to reboot and re-associate.

If that doesn't clear the issue then it is likely a fault within the ASM as no external sensor inputs ( reservoir pressure, height sensors etc.) should trigger the module to output to R1 and try to drive the compressor while the ignition is off.
If the compressor is not making enough pressure, there is a possibility the ASM is not receiving the correct feedback from the pressure sensor in the valve block, however in that scenario ultimately you should be getting a plausibility error if that were the case (which you don't appear to be getting).

Good luck

 

I can't help much re the electronics but there was a fault
a few years ago when there was a bad connection on
the ASM plug/socket.