2012-2018 Audi A6 & S6 Fender Guide: Aluminum Corrosion, Part Numbers, and Replacement

Known Issues for A6 & S6 Fenders (C7)

While fenders are typically damaged by impacts, the C7 platform A6 and S6 have a specific known issue related to corrosion that owners should be aware of.

Technical Service Bulletin: Fender Wheel Arch Corrosion

Audi released Technical Service Bulletin (TSB) V501603 to address reports of corrosion and bubbling paint on the front fender's wheel arch. This issue is not caused by a defect in the metal or paint itself, but by a design flaw where the plastic wheel well liner makes contact with the fender's inner lip. Over time, vibrations and movement cause the liner to rub through the paint and protective coatings. Once the bare aluminum is exposed, dirt and moisture accumulate in the area, leading to galvanic corrosion that appears as bubbling or blistering under the paint.

The official repair procedure involves removing the front bumper and wheel liner, grinding away the corrosion, applying a special epoxy primer and sealer to the edge, and refinishing the fender. When inspecting a vehicle or a used part, this lower wheel arch is a critical area to check.

Common Symptoms of a Failing Fender

Fender failure is almost always the result of physical damage or corrosion. Here’s what to look for:

• Visible Dents, Dings, and Creases: The most common symptom, caused by impacts from other vehicles, shopping carts, or road debris.
• Cracked or Flaking Paint: Often a sign of a minor impact or a poor quality repaint job. On aluminum, this can quickly lead to corrosion if the metal is exposed.
• Bubbling Paint or Corrosion: Pay close attention to the area just above the wheel opening. Bubbles or blisters are a tell-tale sign of the wheel liner corrosion issue described in TSB V501603.
• Poor Panel Gaps: Uneven or wide gaps between the fender, hood, door, and bumper can indicate that the fender is bent or was installed incorrectly after a previous repair.
• Cracked or Broken Mounting Points: These are often hidden from view but can prevent the fender from sitting securely on the vehicle.

Buying a Used 2012-2018 A6/S6 Fender: What to Check

A used OEM fender is often the best value, providing original factory fitment and material quality. However, a thorough inspection is essential before buying.

1. Verify OEM Aluminum vs. Aftermarket Steel

The original fenders are aluminum. Bring a small magnet with you when inspecting a part; it will not stick to the OEM aluminum fender but will stick firmly to a cheaper steel aftermarket replacement. An OEM part ensures correct weight and fitment.

2. Inspect for Hidden Damage

Look beyond the painted surface. Check the back of the fender for signs of previous repairs, such as body filler (Bondo), sanding marks, or overspray. Pay special attention to all mounting tabs and holes—ensure none are cracked, bent, or broken, as this will compromise the final fit.

3. Check for Wheel Arch Corrosion

Run your fingers along the inner lip of the wheel arch where the plastic liner would sit. Feel for any roughness, flaking, or bubbling, which indicates the start of the corrosion issue detailed in TSB V501603. A clean, smooth edge is ideal.

4. Confirm Compatibility

Good news for buyers: the front fenders are interchangeable across the entire generation. This means a fender from a 2012 Audi A6 will fit a 2018 Audi S6, and vice-versa. The body shell did not change in this area during the 2016 (C7.5) facelift, so you can confidently source a part from any 2012-2018 A6 or S6.

5. Plan for Professional Painting

Unless you find a used fender in the exact same color and in perfect condition, assume it will need to be professionally prepped and painted. The cost of painting should be factored into your total budget. Proper preparation of the aluminum surface is critical to prevent future paint adhesion problems.

Fender Replacement Cost & Difficulty

Installation Overview

Replacing the fender is a moderately difficult job. It is not a simple bolt-off, bolt-on process. The front bumper cover and the plastic wheel well liner must be removed first to gain access to all the fender mounting bolts. While the mechanical steps are straightforward, the real challenge lies in aligning the new fender to achieve perfect, even panel gaps with the hood, door, and bumper. This step requires patience and precision.

Recalls and General Vehicle Information

While there are no safety recalls for the fenders on the 2012-2018 Audi A6 and S6, several other important recalls were issued for these vehicles. These include issues with the passenger occupant detection system for the airbags, potential fuel leaks from hoses in the engine bay, and faulty electric coolant pumps. Owners can check the status of their specific vehicle by entering their VIN on the NHTSA website.

Frequently Asked Questions (FAQ)

Technical Specifications & Part Numbers

These fenders are constructed from aluminum. Below are known part numbers, but always verify fitment with the seller using your vehicle's VIN.

• OEM Part Numbers (Audi): 4G0-821-101, 4G0-821-102, 4G0-821-105-E, 4G0821101, 4G0821102, 4G0821102A, 4G0821105, 4G0821105C, 4G0821105E, 4G0821105F
• Partslink Numbers: AU1240125, AU1240125C, AU1241125, AU1241126