B9 S4 Common Problems

In 2018, Audi brought the B9 generation of the A4, A5, and Q5 (as well as the S model equivalent) platforms to the United states. The A4 and A5 continue to use the ubiquitous 2.0t turbo-four, and on the S cars, the long used supercharged V6 was replaced with an all new turbocharged 3 liter V6. While the B9 platform encompasses a wide range of vehicles, in this article we are going to take a look at some common problems owners are seeing on the S4, the performance variant of the A4. 


The new V6 used in the B9 S4 has proven to be a powerhouse. From the factory, the car makes 354 horsepower and 369 pound-feet of torque. That torque number is available below 2400 RPMS, providing a broad torque curve across the power band. 

Combine that with a very tuning-friendly turbocharger setup, and this platform has been pushed into the 700 horsepower range. These power figures were unheard of on the previous generation’s supercharged engine. 

Additionally, the B9 S4 is no longer available with a manual transmission, and the DSG option has been replaced with the robust ZF 8 Speed automatic.

The B9 S4 hasn’t been perfect, though. Unlike the previous generation, which was known for the general reliability of the supercharged V6, the new S4 has a few notable issues you should be aware of, whether you are a prospective buyer or current owner.

Audi 3.0t Turbo V6

Oil Filter Housing

The oil filter housing on the B9 S4 is located on the front of the engine, directly in front of the turbocharger wastegate actuator on the driver’s side of the car. This plastic housing holds the oil filter, allowing for easy access when performing oil changes. 

Unfortunately, this component is prone to leaking. The positioning of the filter housing makes it difficult to easily see the leaks, which can lead to a misdiagnosis. Leaking oil from the housing can sometimes be mistaken for a leaking oil pan, since the oil makes its way down the side of the engine.

Replacing the oil filter housing is fairly in depth, and depending on your technical ability requires the removal of the turbo (which sits in the valley between the cylinder heads). 

Cylinder Six Failure

On both tuned and stock motors, misfires and eventual cylinder six failures have occurred under specific load circumstances. The exact cause of this issue is not fully understood at this point, but adding more power via a tune or other upgrades can make it worse. The video below from Integrated Engineering shows this issue in detail. The vehicle in the video is a stock SQ5, but the drive train is the same as the S4.

PCV Hose Failure

Another common failure on the B9 S4 is the Positive Crankcase Ventilation (PCV) system. PCV is responsible for eliminating positive pressure inside the engine, which can lead to a range of issues. 

The PCV system on the B9 S4 works by routing air from the crankcase back in through the engine’s intake. The PCV block bolts to the driver’s side cylinder head, and can easily be identified by the oil fill cap, which is a component of the block. 

Two hoses run from the PCV block, one leading to a point after the turbo, and another connecting to the intake before the turbo. A check valve controls which hose is used. When the car is off in vacuum (off boost), the post-turbo hose allows air to escape the crankcase. When the turbo is spooled up on throttle, the check valve on the PCV block routes the air from the crankcase into the intake before the turbo, which prevents the pressurized air from being forced back into the PCV system. 

When this check valve fails, things can go sideways. If the post-turbo hose is open when the engine is making boost, the pressurized air will enter the PCV block, causing oil leaks, and in some cases forcing the oil cap to come loose. Audi released a Technical Service Bulletin (TSB) about this problem and issued an improved hose and check valve unit. 

Signs of PCV Failure on the B9 S4

There are three main signs to look for if you suspect your PCV system is starting to fail. 

Oil FIll Cap Seepage

Since a failed PCV check valve allows positive air pressure to flow back into the crankcase, oil will start to appear around the rim of the oil fill cap. 

Oil Leak From the PCV Block

Additional oil leaks can be seen where the PCV block is mated to the cylinder head. The cause of these leaks is the same as the oil cap seepage.

Loose/Lost Oil Cap

This condition is particularly concerning. Excess pressure can force the oil cap to come loose. If the oil cap lifts off the engine while it’s running, oil will spew all over the inside of the engine, potentially causing a fire. 034Motorsport, a VW/Audi tuning company caught a B9 S4 test car on fire due to this problem. Granted, the vehicle was running a large turbo and aggressive tune, but the oil cap issue occurs on stock vehicles as well. The video bellow from 034Motorsport discusses the PCV failure problem in depth.

Rocker Arm Failure

Rocker arm failure plagued the first production year of the B9 S4. Rocker arms are components in the cylinder head, allowing the valves to open and close as the camshaft turns. The rocker arms on the B9 S4, particularly the early models, failed prematurely. Audi revised the design of the rocker arms, making the bearings inside the roller larger. 

If you have a very early B9, it’s possible this issue could arise for you. Generally, the issue first presents as a loud tick (the fuel pump and valve trains on these engines are pretty loud normally, but a failing rocker arm will have a very distinct and noticeable tick), and can eventually lead to severe damage if the rocker fails completely. 


The B9 S4 offers some truly impressive performance, with a very tunable engine and high horsepower potential, a comfortable and advanced interior, and the practicality of a four door sedan. While not as reliable mechanically as the previous generation S4, the B9 is still a solid vehicle. By keeping an eye out for these potential issues, you can ensure your S4 runs like it should for years to come. 

Does your B9 need service? Whether it’s an oil change or rocker arm replacement, Alex’s Autohaus has you covered. Located at 7470 S State Street in Midvale, Utah, we are the Salt Lake Valley’s premiere independent Euro repair shop. Give us a call or schedule an appointment online today!

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