Description

This is a reconditioned Garrett GT15 (part number 454097-5002s) turbocharger for the Audi A4 1.9 TDI models fitted with the AHU or similar engine codes, built between 1995 and 2001. Fully rebuilt at our Birmingham workshop, this unit has been balanced to finer tolerances than the original factory standard and is calibrated ready for installation.

As a core component of your vehicle’s induction system, the turbocharger uses exhaust gas to spin a turbine, which in turn drives a compressor to force more air into the engine. This process, known as forced induction, significantly increases engine power and efficiency. This specific GT15 model is a wastegated turbo, using a pneumatic actuator to control boost pressure by diverting excess exhaust gas past the turbine wheel. Over time, these units can suffer from predictable failures.

Common failure modes for this turbocharger include bearing wear caused by oil contamination or starvation. This leads to excessive play in the shaft, allowing the compressor and turbine wheels to contact their housings, and often results in failed oil seals, causing blue smoke from the exhaust. Another frequent issue is the failure of the wastegate actuator’s diaphragm, which perishes over time, leading to a loss of boost control and poor engine performance. Seizure of the wastegate flap in the turbine housing due to carbon build-up is also a known problem.

At Gap Turbos, our reconditioning service involves a complete strip-down and ultrasonic cleaning of all components. We replace all bearings, seals, and piston rings as standard with new, OEM-quality parts. The central rotating assembly (CHRA) is then precision balanced on our VSR machines at speeds over 150,000 RPM. Finally, the wastegate actuator is tested and calibrated to ensure it performs to the original manufacturer’s specification. We can supply this unit on an exchange basis, or you can book your vehicle in for a complete diagnosis and fitting service at our workshop.

What this turbocharger fits

• Make: Audi
• Model: A4
• Engine: 1.9 TDI
• Engine Codes: AHU, AFN (Note: please verify part number on your original unit)
• Power: 110 HP
• Years: 1995, 1996, 1997, 1998, 1999, 2000, 2001
• OE Part Number: 454097-5002s
• Alternative Part Numbers: 28145702

All our reconditioned turbochargers are supplied with a 24-month warranty. Please contact Gap Turbos with your vehicle registration to confirm fitment and receive a precise quote.

Specifications

Vehicle fitment

• Audi A4 TDI 1.9

Common faults & troubleshooting

• Noticeable loss of engine power, especially when accelerating: This often indicates a failed wastegate actuator diaphragm or a seized wastegate flap, preventing the turbo from generating correct boost pressure.
• Blue or grey smoke from the exhaust, particularly on start-up or overrun: This is a classic symptom of failed internal oil seals, allowing engine oil to leak into the intake or exhaust system and be burnt.
• A loud whistling or siren-like noise from the engine bay: This usually points to worn shaft bearings or a boost leak in the pipework between the turbocharger and the engine’s intake manifold.
• Engine management light on with boost-related fault codes: Diagnostic codes such as P0299 (Turbo/Supercharger Underboost) are a direct indication of a fault with the turbocharger or its control system.
• Excessive engine oil consumption with no visible external leaks: If the engine is using a lot of oil, it may be passing through worn seals inside the turbocharger’s core assembly.

Fitting notes for this unit

• Mandatory Oil Feed Pipe Replacement: The original oil feed pipe must be replaced with a new one. Carbon deposits can build up inside the old pipe, restricting oil flow and causing immediate failure of the new turbocharger.
• Prime Before Starting: Before connecting the oil feed pipe, you must prime the turbo. Use a syringe to inject clean engine oil into the turbo’s oil inlet port while slowly spinning the compressor wheel by hand until oil emerges from the drain.
• Check Engine Oil Pressure: With the old turbo removed, crank the engine (without starting it) until you see a clean, consistent flow of oil from the engine’s feed line. This confirms the engine’s oil pump and supply lines are clear.
• Use All New Gaskets: Do not reuse any old gaskets or studs. Ensure the manifold and exhaust flange surfaces are perfectly clean and flat before fitting the new gaskets provided in the kit to prevent dangerous exhaust leaks.
• Torque Settings: Tighten the manifold nuts and exhaust downpipe bolts to the manufacturer’s specified torque settings and in the correct sequence. Over-tightening can warp the flanges and cause leaks.
• Initial Run-In: After installation, start the engine and allow it to idle for at least 5-10 minutes. This allows oil to circulate fully and lets you thoroughly check for any oil, air, or exhaust leaks before driving the vehicle under load.

Alternative part numbers

This turbo is also referenced by:

• 28145702 — Audi Turbocharger OEM 28145702 (Audi A4 TDI 1.9, AFN/AHU, 110hp)

Frequently asked questions