Understanding the Basics

• Before diving into troubleshooting, familiarize yourself with the car's electrical system layout. Audis have a relatively complex setup, and the owner's manual can be an essential guide.
• Ensure you have the necessary tools on hand, including a multimeter, flashlight, fuses, and a basic toolkit.

Safety First

• Always begin by ensuring the car is on a flat, stable surface with the parking brake engaged.
• Disconnect the negative battery terminal to prevent accidental shorts or shocks while working.

Check the Battery

• Inspect the battery terminals for corrosion, which can impede electrical flow. Clean the terminals if necessary.
• Use a multimeter to check the battery voltage. A fully charged battery should read around 12.6 volts. If it reads below 12 volts, consider charging or replacing it.

Inspect Fuses and Relays

• Refer to the fuse diagram in the owner's manual to identify relevant fuses for the problem circuit.
• Remove the suspect fuse and inspect it visually. A blown fuse will have a broken metal filament. Replace with the correct amperage rating if needed.
• For relays, you can sometimes swap an identical relay from a different part of the car to test whether the relay is faulty.

Examine Wiring and Connections

• Look for signs of fraying, breaks, or corrosion in wiring, especially at connection points.
• Check for any loose connectors that may need securing.
• Wiring harnesses might need to be repositioned or secured if they are rubbing against sharp surfaces.

Test Electrical Components

• Use a multimeter to check continuity and resistance of individual components like switches, motors, and sensors.
• If the multimeter readings don't match the specified values in the repair manual, the component may need replacement.

Onboard Diagnostic System (OBD-II)

• Utilize an OBD-II scanner to read trouble codes from the car's computer system.
• Note the diagnostic trouble codes (DTC) and consult a repair manual or online resources to interpret them.
• Clear the codes and see if they return after fixing the suspected issue.

Seek Professional Help

• If you are unable to resolve the issue, consult a professional mechanic or bring the car to a qualified service center for further diagnosis.
• For complex issues, specialized diagnostic equipment may be needed, which professional services typically have.

By following these steps in detail, you can methodically identify and solve electrical problems in your 2015 Audi A4, or at least have a clearer understanding of the issues before seeking professional help.