To fix a faulty turbocharger in a 2019 Audi A4, follow these detailed steps. Note that some steps involve complex procedures, so it's crucial to have some mechanical expertise or consult a professional mechanic.

Safety First

• Ensure the vehicle is parked on a flat surface, and the engine is cool.
• Disconnect the battery to prevent any electrical mishaps.

Diagnosis

• Use an OBD-II scanner to check for any fault codes related to the turbocharger. This can offer insights into what might be wrong with the system.
• Listen for unusual noises or vibrations coming from the engine bay, which might indicate a problem with the turbo housing or components.
• Check for visible oil leaks around the turbocharger, oil supply, and return lines.

Preparation

• Gather necessary tools such as a wrench set, screwdrivers, ratchets, and torque wrenches. You'll also need replacement parts, which may include new gaskets, hoses, and oil lines.
• Ensure you have the service manual for the Audi A4 to reference exact component specifications and torque settings.

Remove the Turbocharger

• Remove any components obstructing access to the turbocharger, such as engine covers and the air intake system.
• Carefully disconnect all the turbocharger connections, including the air intake pipe, exhaust downpipe, oil supply, and return lines.
• Inspect and mark any vacuum lines or electronic connections to ensure proper reassembly.
• Unbolt and remove the turbocharger from the exhaust manifold. Take note of the bolts; mismatched bolts can cause alignment issues.

Inspect and Clean

• Examine the turbocharger for signs of damage or excessive wear, like cracks, damaged turbine blades, or shaft play.
• Check all removed lines and connections for blockages or damage. Clean them thoroughly or replace them if necessary.
• Inspect the gaskets and fasteners. It’s recommended to replace any gaskets during reassembly.

Install the New or Repaired Turbocharger

• Position the turbocharger onto the exhaust manifold, ensuring it aligns correctly.
• Tighten mounting bolts evenly and according to the specifications in the service manual.
• Reconnect all lines and hoses: begin with the oil supply and drain lines, then move on to the air intake and exhaust pipes.
• Reconnect vacuum and electronic connections, ensuring they match their original marked positions.

Reassemble and Test

• Refill with the appropriate grade of engine oil, as the system may have lost oil during the process.
• Reconnect the battery and start the engine. Allow it to idle and carefully inspect for any leaks or unusual noises.
• Test drive the vehicle to ensure that the turbocharger is functioning correctly, paying attention to power delivery and responsiveness.
• Conduct another scan with the OBD-II scanner to confirm that there are no related error codes.

Post-Maintenance Tips

• Perform regular oil changes and use quality oil approved by Audi to ensure turbo longevity.
• Keep an eye on oil levels, and ensure there's sufficient lubrication to prevent future turbocharger issues.
• Adhere to the manufacturer-recommended service schedule for regular inspections and maintenance.