From the K03-equipped 1.8T to the IS38 on the Golf R, through the RS3 2.5T and RS6 twin-turbo 4.0T: Boost Lab rebuilds the full VW and Audi turbo ecosystem. Oil coking is the defining failure of this platform. We have seen it more times than we can count.
Three distinct turbocharger generations span the VW and Audi lineup. Each has its own bearing architecture, failure patterns, and rebuild considerations.
The K03 and K03S were the workhorses of the 1.8T 20V era. The K03 uses an 11-blade compressor wheel; the K03S upgrades to 8 blades. The two share the same footprint and are effectively interchangeable. Actuator spring rate (65N vs 85N) varies by power output. Also covers EA113 2.0T (BPY/BWA) and EA888 Gen 1/2 applications.
Two configurations that are not interchangeable. The K04-001 (transverse) is a direct bolt-on upgrade for K03/K03S on transverse 1.8T. The K04-023 is fitted to Quattro AWD platforms (S3 210hp, TT 225 Quattro) with a different exhaust manifold and downpipe geometry.
The MQB platform introduced the IHI IS-series. IS12 covers 1.8T; IS20 is standard on 2.0T GTI; IS38 is factory on Golf R, S3, TTS, and Arteon. The IS38 is the most popular single upgrade in the VAG community: a direct bolt-on for any IS20 application with a tune. Thrust bearing wear is the primary rebuild item on tuned IS20 and IS38 units.
The RS3 and TT RS use Audi's 2.5T inline-5 TFSI with a single twin-scroll IHI turbocharger. The RS6, RS7, S6, S7, and S8 4.0T use twin BorgWarner turbos positioned in the valley between cylinder banks (hot-vee configuration), which creates unique oil drain challenges and elevated thermal load.
A pair of K03 turbos in a twin configuration. Both should be rebuilt as a set. The 2.7T is known for oil sludge accumulation in the valley between cylinder banks, directly impacting turbo oil feed quality.
The TDI lineup spans 1.9 TDI (BorgWarner VNT with common actuator failure), 2.0 TDI PD and CR (BorgWarner K03 TDI and various), and 3.0 TDI (BorgWarner twin sequential with LP and HP stages). All TDI turbos are oil and water cooled and require full cooling circuit inspection at rebuild.
Search by model, turbo designation, or engine code. Use this table to identify your turbo before submitting a rebuild request.
| Turbo | Application | Engine / Code | Mfr | Notes |
|---|---|---|---|---|
| K03 / K03S (1.8T / 2.0T) | ||||
| K03 | Audi A4 B5 1.8T 150hp | AEB / ANB | KKK/BW | 11-blade compressor, 65N actuator |
| K03S | Audi A3 8L / A4 B6 1.8T 150hp | AUM / AWW | KKK/BW | 8-blade, drive-by-wire |
| K03S | Audi TT 8N 1.8T 180hp | AWP / AMK | KKK/BW | 85N actuator, higher boost |
| K03S | Audi S3 8L 210hp | AMK / BAM | KKK/BW | FWD only; AWD gets K04-023 |
| K04 (Upgrade / AWD) | ||||
| K04-001 | VW Golf / Jetta / A3 1.8T upgrade | Multiple | KKK/BW | Direct K03 replacement, bolt-on |
| K04-023 | Audi S3 8L Quattro / TT 225 Quattro | AMK / BAM / APX | KKK/BW | AWD platform only; different downpipe |
| K03 / K03S (1.8T / 2.0T) | ||||
| K03 (BWA) | VW Golf Mk5 GTI / Jetta GLI 2.0T | BPY / BWA / AXX | BorgWarner | EA113; K04 upgrade needs injectors |
| K03 (EA888) | VW Golf Mk6 GTI / Jetta GLI | CBFA / CCTA | BorgWarner | EA888 Gen 1; chain-driven cam |
| K03 (EA888) | Audi A4 B8 / A5 / Q5 2.0 TFSI | CDNB / CAEB | BorgWarner | Longitudinal; water-cooled bearing |
| K03 (EA888/2) | VW Passat B7 / CC 2.0T | CBFA / CCZA | BorgWarner | Gen 2; similar to Gen 1 turbo |
| IS12 (MQB 1.8T) | ||||
| IS12 | VW Golf Mk7 1.8T / Jetta 1.4T/1.8T | CPMA / CHPA | IHI | MQB 1.8T; baseline MQB turbo |
| IS12 | Audi A3 8V 1.8 TFSI | CJSA / CJSB | IHI | MQB platform |
| IS20 (MQB 2.0T GTI) | ||||
| IS20 | VW Golf Mk7/7.5 GTI | CHHB / CHHA | IHI | Stock 220hp GTI; upgrade to IS38 w/ tune |
| IS20 | VW Jetta GLI A7 / Tiguan MQB | CHHB / CZPB | IHI | Same unit as GTI |
| IS20 | Audi A3 8V 2.0 TFSI / TT Mk3 2.0T | CJXB / CJXA | IHI | MQB longitudinal; IS38 bolt-on |
| IS38 (Golf R / S3) | ||||
| IS38 | VW Golf R Mk7 / Mk7.5 | CJXC / DKZ | IHI | Factory 310hp; thrust bearing wear on tune |
| IS38 | VW Arteon 2.0T | DNUE | IHI | Same family as Golf R |
| IS38 | Audi S3 8V / TTS Mk3 | CJX / CJXB | IHI | Factory fitment; IS20 upgrade target |
| RS3 / TT RS 2.5T | ||||
| 2.5T IHI | Audi RS3 8P / 8V / TT RS Mk2 | CEPA / CZGC | IHI | 5-cyl twin-scroll; single unit |
| 2.5T IHI | Audi RS3 8Y (2022+) | DNWA | IHI | Updated 5-cyl; 400hp factory |
| Audi 2.7T Biturbo (K03 Twin) | ||||
| K03 Twin | Audi S4 B5 / B6 2.7T | AGB / AZB / BES | KKK/BW | Rebuild as matched pair |
| K03 Twin | Audi A6 C5 2.7T / Allroad 2.7T | AGB / AZB | KKK/BW | Oil sludge inspection required |
| RS6 / RS7 / S6 / S7 4.0T | ||||
| BW 4.0T Twin | Audi RS6 / RS7 C7 4.0T TFSI | CGTA / CTBA | BorgWarner | Hot-vee; both turbos rebuild together |
| BW 4.0T Twin | Audi S6 / S7 / S8 4.0T TFSI | CGTA / CTBA | BorgWarner | Same twin as RS6/RS7 |
| BW 4.0T Twin | Audi RS6 / RS7 C8 (2020+) | DGGB / DDYS | BorgWarner | Mild hybrid; updated turbo architecture |
| Other VW/Audi | ||||
| BW VNT | VW Jetta / Golf / Passat 1.9 TDI | ALH / BEW / BRM | TDI | Variable nozzle; actuator failure common |
| TDI Diesel | ||||
| BW K03 TDI | VW Golf / Jetta 2.0 TDI PD | BKD / BMN | TDI | Pumpe Duse injection; different oil spec |
| Other VW/Audi | ||||
| BW 2.0 TDI | Audi A3 8P / Golf Mk6 2.0 TDI CR | CBAA / CBAB | TDI | Common rail; revised bearing housing |
| BW 2.0 TDI | Audi A4 B8 / Q5 2.0 TDI | CAHA / CAGA | TDI | Water-cooled bearing housing |
| BW Twin Seq. | Audi A6 C6/C7 / A7 / Q7 3.0 TDI | CLAA / CRCA | TDI | Low-pressure + high-pressure stages |
| BW Twin Seq. | Audi A8 3.0 TDI / Q7 3.0 TDI | CCWA / CRCD | TDI | Full cooling circuit inspection required |
No results? Contact us at sales@theboostlab.com with your model and engine code.
The predominant VW/Audi failure mode. Hot shutdowns without cooldown bake residual oil into hard carbon deposits in the bearing housing. Extended OEM oil change intervals accelerate this. Coking restricts oil passages, reduces bearing lubrication, and eventually causes bearing seizure. At teardown we flush and inspect oil passages before any rebuild quote is issued.
Extremely common on the 2.0T FSI K03 (BPY/BWA engine codes). The actuator rod seizes or the diaphragm fails, causing the wastegate to stick open or closed. Stuck-open causes chronic underboost and limp mode. Stuck-closed causes overboosting. The actuator is inspected and replaced at every rebuild.
The IS20 and IS38 thrust bearing is the limiting component under sustained high-boost operation on tuned vehicles. Thrust bearing wear presents as increased shaft endplay and compressor wheel contact marks. Tuned MQB GTI and Golf R owners running stage 2 or higher should include periodic turbo inspection.
The 2.7T biturbo is notorious for oil sludge accumulation in the valley between cylinder banks, directly affecting turbo oil feed quality. Any VW or Audi with a history of infrequent oil changes should have oil passages flushed before turbo rebuild.
Intake-side debris from deteriorated air box components, collapsed intake hoses, or a failed air filter. Turbine-side FOD from failing catalytic converter substrate is also seen on high-mileage units. Both compressor and turbine wheel condition are documented at teardown.
The RS6/RS7 and S6/S7/S8 4.0T TFSI positions both turbos in the valley between cylinder banks (hot-vee). This creates challenging oil drain geometry and elevated thermal load. Both turbos rebuild as a set. Full oil circuit inspection is mandatory on these applications.
A turbo out of the car is an opportunity. Both of the most popular VAG performance upgrades are direct bolt-on swaps requiring only a tune.
The K04-001 is a direct bolt-on replacement for the K03 and K03S on transverse 1.8T applications. It flows more and supports higher boost levels than the K03S. On EA113 2.0T applications (BPY/BWA), K04 upgrade requires injector upgrades as the factory injectors cannot flow enough fuel at K04 boost levels. K04-001 (transverse) and K04-023 (AWD Quattro) are not interchangeable. Confirm your drivetrain before ordering.
The IS38 is a direct bolt-on replacement for the IS20 on all MQB applications. Factory fitment on the Golf R and S3 means it is a production-proven unit at significantly higher output. Tune required: running an IS38 on IS20 software causes boost control issues. The ECU must be calibrated for the IS38 wastegate characteristics before the car is driven.
Start a rebuild request online. Ship your turbo to Dade City, FL and we handle the rest. K03 through IS38, RS3 through RS7, TDI to 4.0T twin.
Start Your Rebuild37833 Pineapple Ave Unit A • Dade City, FL 33523 • sales@theboostlab.com