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Changing the air compressor / replacing the compressor piston ring (2002-2005 only)

Discussion in 'Technical Archive' started by charliedurrant, Oct 21, 2014.

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  1. charliedurrant

    charliedurrant Member

    Nov 27, 2011
    Likes Received:
    Broadstairs, Kent, UK
    The air compressor gets worn over time and can result in Air Suspension Inactive dash warnings. Diagnostics will are best to really diagnose the issue (unless leaks can be heard) but a worn compressor is not an uncommon problem.

    When the output is low it can overheat and the ECU will shut it down, also if the output is really pathetic the air cylinder will take too long to fill and another error will result - as said diagnostics will be required. Checking output however is relatively easy:

    Checking output

    Output can be checked by removing the output line from the compressor which is held by a collet.


    The second video below titled "Changing the compressor" below shows the removal of the output line in more detail.

    The air compressor now needs to be forced on by shorting out the wires the are normally controlled by a relay. The relay behind the right hand side panel in the boot / trunk:


    The relay to remove is the black one with the diagonal molded plastic line on it


    Remove the replay and short out the two large spade connectors:




    Once the compressor kicks in if you can easily hold your finger over the outlet then the output is not up to scratch.

    Replacing the piston ring - wabco compressors: 2005-2005 L322 Only

    If output is low then the first thing to do is to try replacing the piston ring:


    If the cylinder is scored then changing the ring will give some extra use. I got 20,000 miles extra by changing a ring however if there is scoring at some point the compressor will need to be changed as Wabco kindly do not supply replacement cylinders.

    Changing the compressor


    Video kindly provided by Powerful UK

    If you are running LPG the compressor won't be in the place shown in the video as your spare wheel space will be used for the tank. If you can't find it then just pump the suspension up and down and listen for where it is!

    Resetting fault codes

    You were most likely checking output because of the in dash warning "Air Suspension Inactive". To reset the warning see:



    As said at the start, diagnosing air suspension issues really requires diagnostics (I use Storey Wilson's AllComms) unless obvious leaks can be detected or you have a lot of time to test all the components! However, testing pump output is a simple DIY exercise and could save you a penny or two by replacing the piston ring or the labour costs of fitting a replacement pump.

    Last edited: Oct 23, 2014
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