Audi A5 Brake Light Fail - How To Diagnose And Fix

By Nick Marchenko, PhD

Brake light issues in vehicles are common but can lead to serious safety hazards if not addressed promptly. The Audi A5 is no exception, and owners may encounter problems where the brake lights either fail to illuminate or the dashboard indicates a fault despite the lights appearing to work. This guide, drawing upon shared experiences and solutions, provides a comprehensive approach to diagnosing and fixing brake light problems in your Audi A5.

Preliminary Checks

Before diving into the more technical aspects, perform these initial checks:

• Inspect the Bulbs: Ensure that the brake light bulbs are functioning correctly. Swap the bulbs into a different socket (e.g., the blinker section) to test if they light up.
• Check for Dashboard Indicators: A dashboard warning light for brake light failure is a common indicator of a problem, even if the lights seem to work.

Check what bulbs are used in your Audi A5 in our Bulb Size Chart:

• 2018;
• 2017;
• 2016;
• 2015;
• 2014;
• 2013;
• 2012;
• 2011;
• 2010;
• 2009;
• 2008;

Step 1: Inspect Bulb Contacts and Holders

One of the most frequent causes of brake light failure is issues with the bulb contacts or holders:

•     Rusted or Corroded Contacts: The metal contact at the base of the bulb can rust or corrode over time, leading to poor connection and bulb failure. Inspect the contacts for any signs of rust or corrosion.
•     Damaged Bulb Base: A damaged base can prevent proper electrical contact. Look for any signs of overheating or physical damage to the bulb's base or solder.
•     Bulb Holder Issues: The bulb holder itself may be damaged, corroded, or cracked, affecting the connection and function of the brake lights.

How to Fix:

    Clean any rust or corrosion from the bulb contacts with a suitable cleaning agent or fine sandpaper.
    Replace the bulb if the base is damaged or the solder appears melted.
    Inspect the bulb holder for damage or corrosion and replace it if necessary.

Step 2: Electrical Troubleshooting

If the bulbs and their contacts are in good condition, the problem may lie within the electrical system:

•     Check the Fuses: Ensure all relevant fuses are intact and have not blown.
•     Brake Pedal Switch: Confirm that the brake pedal switch is functioning. If the dashboard indicator lights up upon pressing the brake but the brake lights don't illuminate, the switch itself is likely not the issue.
•     Continuity Testing: Use a multimeter to test the continuity of the wires and the tail light assemblies. Start testing at the bulb socket, then move to the harness connection and trace the wires back towards the brake pedal switch.

How to Fix:

•     Replace any blown fuses and retest the brake lights.
•     Perform voltage checks with a multimeter. You should find approximately 12 volts at the socket when the brake pedal is pressed. A lack of voltage could indicate a wiring problem.
•     Inspect the brake light switch and replace it if defective.

Step 3: Verify Bulb Type and Filament Condition

Incorrect bulb type or filament issues can also cause brake light failures:

• Dual Filament Bulbs: Ensure you are using the correct dual filament bulbs for brake/tail light functionality. Single filament bulbs will not work correctly in these sockets.
• Filament Damage: A damaged or broken filament in the bulb can prevent the brake light portion from illuminating while allowing other functions (e.g., tail lights) to work.

How to Fix:

• Double-check that the correct bulb type is installed. For brake lights, dual filament bulbs are typically required.
• Replace any bulbs with damaged filaments.

Additional Tips

• DIY Electrical Testing: Familiarize yourself with basic electrical troubleshooting using a multimeter. This can save time and avoid unnecessary parts replacement.
• Consult Wiring Diagrams: For complex issues, consulting a vehicle wiring diagram can provide clarity on the electrical pathway for brake lights, aiding in pinpointing specific faults.

By following these steps, most Audi A5 brake light issues can be diagnosed and resolved with a bit of patience and DIY effort. Always prioritize safety and ensure any electrical work is done with the vehicle off and keys removed from the ignition.

See Also:

• Audi A5 Typical Problems: TDI Engine Weak Points
• Purifying Power: A Guide to Cleaning Your Audi A5 Engine for Peak Performance
• What Does p1564 Audi A5 Mean?

Nick Marchenko, PhD

Industrial Engineer & Automotive Content Specialist

Nick writes in-depth guides on car clubs, engine specs, vehicle ownership, and modifications, combining engineering knowledge with automotive passion.

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