The B9-generation Audi A4 and S4 use a cleaner and more technical exterior design than the earlier B8.5 platform. Sharp lower-bumper openings, defined body lines and a relatively restrained Sedan profile allow owners to choose either subtle OEM-plus details or more pronounced front, rear and trunk upgrades.
This collection brings together selected 2017–2019 Audi A4 / S4 B9 carbon fiber parts, including products for the A4 Base, A4 S line and S4 Sedan. Available categories include full front lips, bumper vents, fog lamp covers, rear diffusers and several trunk spoiler profiles. Each component must be selected according to the original bumper, trim, installation area and product-specific model years.
What Makes the Audi A4 and S4 B9 Exterior Different?
The B9 moved the A4 and S4 toward a sharper, more geometric exterior. Instead of the smoother lower sections seen on earlier generations, the B9 front bumper uses clearly separated center and side openings. This makes the exact location of each upgrade especially important.
A full front lip follows the lower perimeter of the bumper. Front bumper vents and fog lamp trims sit around the outer openings, while smaller canards or fins emphasize only selected corners. These parts may appear together in search results, but they are not interchangeable and may not use the same mounting method.
The rear of the B9 also varies significantly by trim. The factory lower valance and exhaust layout determine whether the vehicle requires an A4 Base diffuser, an A4 S line or S4 design, or a diffuser supplied with separate splitter extensions.
B9 Pre-Facelift vs the Later B9.5 Update
This collection is structured for selected 2017–2019 B9 pre-facelift Sedan applications. Later A4 and S4 models received updated exterior details, so front lips, vent trims and rear diffusers should not be selected only by the broader B9 platform name.
Bumper-mounted parts are the most sensitive to the update. The lower grille shape, outer openings, bumper corners, mounting edges and rear valance must match the product photos and fitment description. A visually similar part can still use different tabs, screw positions or contact surfaces.
Some individual listings on this page include 2020 because model-year and exterior-update timing can vary by product and market. Follow the exact product page rather than assuming every item in the collection has the same final fitment year.
Later-model customers should also review our 2020–2022 Audi A4 / S4 B9.5 parts collection before placing an order.
Audi A4 B9 Base vs A4 S line vs S4 Fitment
The original bumper configuration is the most important compatibility detail for this collection. An Audi A4 B9 Base does not use the same lower front and rear bumper design as an A4 S line or S4. A product shaped around one bumper cannot be treated as a universal Audi A4 B9 part.
Dedicated A4 Base products on this page include a front lip, front bumper vents and a rear diffuser. They follow the standard A4 bumper and should not be selected for an A4 S line or S4 unless the individual listing explicitly confirms that sport-bumper application.
Many sport-bumper products are grouped for the A4 S line and S4, but this does not mean every exterior component is shared. Check the complete bumper, outer vent design, lower grille openings, rear valance and exhaust positions. Previous repairs or bumper conversions can also change the installation area from the original factory configuration.
Choosing an Audi A4 B9 or S4 B9 Front Lip
Front lips are one of the largest product groups in this collection. Several designs are available for the Audi A4 B9 S line and S4, while a separate lip is listed for the A4 Base bumper.
The available designs may differ in center projection, overall width, corner angle, number of sections and how closely they follow the factory bumper. A lower-profile lip keeps more of the original Audi shape visible, while a wider or more pronounced design creates a stronger visual line across the front of the Sedan.
Similar product titles do not mean the physical designs are identical. Compare the front view, side profile, outer corners and underside mounting points shown in the product photos. One listing also has a narrower 2019-specific application, so its individual year range must be followed.
ground clearance should be considered before ordering an audi a4 b9 front lip or audi s4 b9 front lip. Lowered suspension, steep driveways and existing bumper damage can affect alignment and everyday use. Complete a full test fit before drilling or applying permanent adhesive.
front bumper vents, fog lamp covers and canard-style trim
front bumper vents and fog lamp covers target smaller sections of the b9 front fascia than a full lip. They are useful for owners who want to add carbon fiber around the outer bumper openings without extending the entire lower edge.
an audi a4 b9 front bumper vent generally follows the shape of the side intake or factory trim. A fog lamp cover surrounds a more specific outer opening, while a canard or fin adds a smaller projecting detail. The number of pieces and exact mounting position should be checked before ordering.
this collection contains separate vent products for a4 base and a4 s line or s4 bumpers. An a4 s line vent or fog lamp cover should not be selected for an a4 base simply because both cars are b9 sedans.
add-on vs replacement front vent designs
some front vent products are available in add-on and replacement-style versions. An add-on component attaches over the existing factory trim and leaves the original part underneath. A replacement component requires the factory trim to be removed and must match its clips, edges and internal mounting points.
the two constructions can look similar in product photos, but installation effort and final edge alignment May differ. Review the selected variant, package contents and installation photos before checkout.
test fit both left and right pieces at the same time. Small differences in height, angle or distance from the bumper opening become more noticeable when the two sides are viewed together.
audi a4 and s4 b9 rear diffuser fitment
rear-diffuser fitment depends on the original rear bumper, lower valance and exhaust configuration. An audi a4 b9 rear diffuser for the base bumper should not be assumed to fit an a4 s line or s4.
products for the sport bumper follow different outer corners and exhaust openings. Check the number, position and width of the exhaust cutouts, especially when the vehicle has aftermarket exhaust tips or a modified system.
also confirm whether the selected diffuser replaces the factory lower valance or attaches to an existing bumper section. Replacement products must match the original tabs and screw points, while add-on products use a different installation surface.
standard diffuser vs diffuser with splitters
the collection includes several s4 rear-diffuser designs. A standard diffuser changes the main lower center valance. A diffuser with splitters combines the central section with additional outer extensions or more pronounced corner details.
customers comparing these products should review the number of pieces and the completed rear view. A multi-piece design May require more alignment during installation and creates a different result from a simpler one-piece audi s4 b9 rear diffuser.
additional splitters do not make the diffuser universal. The central section must still match the original s4 or confirmed a4 s line bumper and exhaust arrangement.
Choosing an Audi A4 or S4 B9 Trunk Spoiler
Trunk spoilers are the largest style-based category in this collection. Several products may share the same general vehicle range but use different heights, center curves, outer tips and rear profiles.
A low-profile lip follows the trunk edge closely and creates a restrained OEM-plus result. A higher-kick, ducktail or GT-style design is more visible from the side and rear three-quarter view. Customers should compare the actual installed shape instead of choosing only by the general phrase “Audi A4 B9 trunk spoiler.”
Material and condition options must also be checked. Some listings include carbon fiber and glossy black FRP variants, while others contain new and small-flaw options. The selected variant should match the finish and condition the customer expects to receive.
B9 and B9.5 Shared-Fitment Trunk Spoilers
Several trunk spoilers on this page list a wider 2017–2023 range and are shared between B9 and B9.5 Sedan applications. This is different from front lips and diffusers, which depend more directly on the exterior bumper design.
A shared spoiler can appear in both generation collections, but the two collection pages should not target the same keywords. This page remains focused on 2017–2019 B9 owners, while the product page explains the complete B9 and B9.5 fitment range.
Confirm the Sedan trunk shape and compare the spoiler’s outer ends, center curve and contact surface with the listing photos. A broad year range does not replace a direct visual compatibility check.
Confirm Your 2017–2019 Audi A4 or S4 Before Ordering
Before checkout, confirm the vehicle year, A4 or S4 model, Base or S line trim, Sedan body style, original bumper and intended installation area. Review the product page for the exact year range, material, finish, number of pieces and add-on or replacement construction.
Owners comparing the previous generation can browse our 2013–2016 Audi A4 / S4 B8.5 parts . To compare all available generations, visit Audi A4 / S4 parts by generation . Other Audi models can be found through our Audi parts by model collection.
When compatibility remains uncertain, send the vehicle year, trim and clear photos through our Audi A4 / S4 B9 fitment support page. Useful photos include a full front or rear view, a direct photo of the original bumper and a close image of the intended mounting area.
Complete a test fit before final installation. Larger front lips and rear diffusers should normally be installed by an experienced automotive body or modification workshop to support correct alignment.
