VAG Turbo Families – VW/Audi/Seat/Skoda 1.8T 20V R4 transverse engines

There are three names you will find when looking for turbos on 1.8T 20V transverse engines. K03, K03S and K04. Each one being bigger than the one before.
K04 comes in two flavours: K04-001 and K04-023.



K03, K03S and K04-001 are direct replacements of one another. The K04-023 comes with a completely different intake system, exhaust manifold and requires a different downpipe. This difference exists because it was only installed on 4WD drive platforms, where the transmission axle makes things different in the exhaust geometry.

Be careful, these turbos are not the same with the K03 and K04 installed on longitudinal engines, like the Audi A4 and VW Passat.

Transverse engines exist in the following very popular models amongst the VAG group:

  • Audi A3 8L (K03 on mechanical throttle, K03S on drive-by-wire systems)


  • Audi S3 8L (K04-023 on all versions)
  • Audi TT 8N (Only drive-by-wire system exist. K03S on 150hp and 180hp versions, K04-023 on 210hp/225hp versions)
  • VW Golf Mk IV (K03 on mechanical throttle, K03S on drive-by-wire systems)
  • VW Bora (K03 on mechanical throttle, K03S on drive-by-wire systems)
  • Seat Leon MK I (K03 on mechanical throttle, K03S on drive-by-wire systems, K04-023 on Cupra)
  • Seat Ibiza (K03 on mechanical throttle, K03S on drive-by-wire systems)
  • Skoda Octavia (K03 on mechanical throttle, K03S on drive-by-wire systems)

Now a few rules so that you can identify them more easily

The first generation of transverse 1.8T 20V engines with a mechanical throttle had K03 turbos. Up to model year 2000, everything used K03.
K03 turbo on the following engine codes:

  • AGU (on VW Golf 4 GTI, Audi A3, Skoda Octavia)
  • AJH (VW Sharan, Seat Alhambra)

With the appearance of modern electronics and OBD2-compliant systems, throttle control became fully electronic. Drive-by-wire systems marked the appearance of K03S, which is a significantly larger turbo than the K03.

K03S turbos exist on engine codes:



  • AUM (Golf, Octavia, A3, Leon – 150hp)
  • AUQ (Golf, Octavia A3, RS, Leon – 180hp)
  • BBU
  • BJX
  • BFB
  • BVP
  • AWV
  • AWP (VW Jetta)

Upgraded versions of the 1.8T 20V engines with 210hp or 225hp appeared with OBD2 compliant electronics and Drive-by-wire systems too. They always use a K04-023 turbo because they are all 4WD:




  • AMK (210hp)
  • AMU
  • BAM (Audi TT and S3 – 225hp)
  • APX (Audi TT – 210hp)
  • APY (Audi S3 – 210hp)
  • BFV


  • VGA Posted March 26, 2019 12:07 am

    And code engine ARX?

  • Panos Posted July 16, 2019 8:00 pm

    ARX in the haldex AWD variants is equipped with the K03s

  • 2stroke Posted September 5, 2019 5:52 pm

    What about the K03 / K03s / K04 ???
    installed on longitudinal cars like:
    * Audi A4 “B5” ( 1995-2000 )
    * Audi A4 “B6 & B7” ( 2001-2008 )
    * Audi A6 “C5”
    * Seat Exeo ( 2009-2010 )
    * Skoda Superb ( 2002-2008 )
    * VW Passat ( 1997-2005 )

  • Luke Posted April 15, 2020 4:54 pm

    Please help as in a rut.
    2002 vw sharan 1.8t AWC looking at turbo replacement.

    Been told k04015 will fit
    And wont fit
    Been told the same for k04001

    My turbo is knackered and looking at upgrade maybe k03s

    • Stelios Alexandrakis Posted April 16, 2020 12:30 am

      K04-015 is used on longitudinal engines. K04-001 is for transverse engines but because of its rather old design, is no more efficient nor powerful compared to a K03S.
      Unfortunately I have never seen a Sharan 1.8T AWC to recommend you what to get. Depending on your engine’s orientation, you can choose from the above.

  • Stratos Posted October 28, 2020 1:21 pm

    I have an 1,8T 20v 4×4 Skoda Octavia estate (combi). She is equipped with the K03s turbine. Which of the K04 family turbines will be a straight swap on without any other modifications needed?

    Thank you in advance

  • JW Posted April 30, 2023 10:37 am

    There is also K04-022 on APX, providea 225hp as BAM bjt has no temp sensor.

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