Audi B9 S4

The 5 Most Common Audi B9 S4 Problems

Chandler Stark

Meet Trey

Trey is an automotive enthusiast and has a huge passion for Volkswagen and Audi vehicles of all kinds. His enthusiasm started with the MK5 GTI, and he has massively expanded his knowledge over the years. When Trey is not delivering high-quality and in-depth content, we can usually find him working in his garage on his modified Genesis coupe. Trey created VW Tuning several years ago, and he is the primary visionary behind the content.

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Whether you hear or see B9 Audi S4, Audi S4 B9, or Audi B9 S4, there are all referring to the latest version of Audi’s S4 (2017 – present). This new vehicle was announced by Audi in 2015 and was released for sale to the public in 2017 and is still sold today. The new B9 included an updated modern facelift, new wheels, and two new engines compared to its predecessor, the B8/B8.5 S4.

The engines featured in the B9 S4 are a new 3.0 V6 TFSI (Engine code CWGD) or a 3.0 V6 TDI in Europe only (2019 and later | Engine Code DEWB). The 3.0 TFSI puts out 354 hp and 368 lb-ft of torque using a single twin-scroll turbocharger, while the 3.0 TDI puts out 351 hp and a whopping 519 lb-ft of torque. Both engines are equipped with an eight-speed quattro® Tiptronic® automatic transmission with AWD.

Since this vehicle has two different engines, we will try to distinguish which common problems are most relevant with which engine. Before going into the B9 S4 common problems guide, PLEASE make sure the parts and DIY guides listed apply to your specific vehicle! Let us know in the comments if you need help looking for parts or guides and we will assist in any way we can!

Audi B9 S4 Problems

  1. Misfires: Injectors, coil packs, and spark plugs
  2. Water Pump/Thermostat Failure
  3. PCV Valve Failure
  4. Carbon build-up
  5. Deteriorating bushings

1. Engine Misfires: Ignition coil/coil pack failure

Ignition coils seem to be are a common problem with a lot of vehicle engines nowadays. Since there are 6 cylinders in the 3.0’s, there are 6 ignition coils. Within an ignition coil, you will find a spark plug, which can also fail from normal wear and tear (heat) or from enhancing engine performance rapidly. The purpose of the ignition coil is to transfer electricity from the battery to the spark plug to create combustion. When any of the 6 coils are faulty, several things could go wrong (mainly misfires), and it is important to address the issue right away.

Ignition coils tend to last about 50,000 – 70,000 miles depending on how well the vehicle is maintained and if it remains stock. Whenever you bring engine upgrades into the mix, the reliability of these coils is dampened due to irregular engine performance. If you end up tuning your vehicle, we would advise moving to aftermarket coils/plugs so that they run cooler.

Symptoms of Coil Packs/Spark Plugs Failure:

Coil Pack/Spark Plug Replacement Options:

When it comes to replacing your ignition coils or spark plugs, we would highly advise changing all of them at once. It may sound expensive to replace all 6, but it will save you from many headaches in the long run. Changing these is actually a pretty simple DIY, but if you’re looking to take it to the shop, you would be looking at a bill around ~$600.

Buy Here: S4 B9 OEM Ignition Coil Replacement
Buy Here: S4 B9 OEM Spark Plug Replacement

DIY Difficulty: Easy
Spark Plug Written DIY Guide:

2. Water Pump/Thermostat Failure

Water pumps and thermostats seem to be a weak point when it comes to Audi’s, mainly due to the components that they are made of. These two parts are crucial for the engine cooling system. A water pump carries coolant from the radiator to the engine to ensure the engine temperature is at optimal levels. A thermostat in an engine is just like a thermostat in a house, it monitors and regulates the engine’s temperature to ensure it stays at the most optimal level. If either fails, your vehicle will overheat and will need immediate attention to reduce further engine damage.

The main reasons these fail are normal wear and tear or improper maintenance of the cooling system. Hypothetically speaking, both the thermostat and water pump should last up to 75,000 miles but should be looked at every 30,000 miles for preventative measures.

Symptoms of Water Pump/Thermostat Failure:

  • Engine overheating
  • Steam coming from under the hood
  • Erratic temperature changes
  • Whining noise coming from the engine
  • Low coolant levels

Water Pump/Thermostat Replacement Options:

If you know your way around an engine, this is a relatively easy DIY. Something that we suggest is replacing your water pump and thermostat at the same time because generally, these have the same maintenance schedules. If you’re looking to get this replaced at a dealer, you would be looking for a cost of around ~

Buy Here: S4 B9 OEM Water Pump Replacement
Buy Here: S4 B9 OEM Thermostat Replacement

DIY Difficulty: Easy

3. Engine Oil Separator Failure

The engine oil separator’s purpose is to extract oil droplets from the air before it goes back into the intake manifold, which prevents premature combustion in the engine. Without a functioning engine oil separator, this could lead to carbon buildup at a much quicker pace. This part is common to fail at least once in your vehicle’s lifetime and should be looked at every 60,000 miles. The main reason these fail is due to normal wear and tear.

Symptoms of Engine Oil Separator Failure:

  • Rough idle
  • Engine misfires
  • Whistling noise coming from the engine
  • Fault codes: P0171, P0507, P0300 – P0306
  • Lean AFR (air-to-fuel) conditions

Engine Oil Separator Replacement Options:

Regardless, if the engine oil separator fails or is stuck in the open or closed position, you will want to replace the valve to avoid future issues. This is a relatively easy DIY if you have the proper tools. The engine oil separator itself is only $70, but we advise getting the ECV and the seal for another $12.

Buy Here: S4 B9 OEM ECV Valve Replacement

DIY Difficulty: Easy

4. Carbon Buildup

To be honest, carbon buildup is hard to avoid because it naturally happens on all direct injection engines. What happens is fuel is sprayed into the combustion chamber through the valves and intake manifold causing carbon buildup or gunk to deposit. This can cause your engine to have a loss in performance due to the difficulty in “breathing”.

If you drive your vehicle to work, the store, or anywhere that is a short distance on a normal occurrence, buildup may occur quicker because you are not burning away the buildup as often. We list some preventative measures below, but we advise getting them cleaned or at least inspected every 50,000 miles.

Symptoms of Carbon buildup:

  • Reduced fuel economy
  • Cold start misfires
  • Reduced engine performance
  • Knocking engine
  • Engine stalls

Ways to Prevent Carbon Buildup in the Intake Valves:

  • Run your engine for an extended period of time (~30 mins @ 3000 RPMs)
  • Use the highest quality fuel possible (+93 or higher)
  • Manually scrubbing the valves
  • Get valves professionally walnut blasted

Preventative maintenance should be made on the intake valves at least every 45,000 miles. If there happens to be a lot of buildup, we would advise getting it professionally cleaned unless you happen to have the proper machinery. If you are looking to take it to a shop to get walnut blasted, you will be looking at around ~$600, but it is well worth and you WILL tell a difference.

DIY Difficulty: Intermediate to Difficult

5. Deteriorating Bushings

Deteriorated bushings, unfortunately, are a pretty common occurrence with the B8 & B9 platform in Audi’s. There are many different bushings, but the ones we are referencing are located on the control arms on your suspension and they isolate vibration, provide cushioning, and reduce friction in the metal components of the suspension. If they fail or are deteriorating, it could cause serious damage to your suspension if not addressed shortly after.

These bushings are not the most reliable out of the factory, but for the most part, they fail due to normal wear and tear. If your bushings seem to be fine, we advise getting them checked out at least every 75,000 miles.

Symptoms of Deteriorating bushings:

  • Clunking or scraping noises when driving
  • Uneven tire tread wear
  • Reduced handling and braking
  • Vibrating steering wheel

Bushings Replacement Options:

When it comes to deteriorating bushings, we would advise replacing not only the bushings but the entire control arm. This may be more expensive, but it will save you money in the long run. The B9 S4’s front-end control arms seem to be a common problem from the factory. This is a difficult DIY because you would need a car jack and know how to deal with suspension, but it is possible. If you were to take it to a shop, you would be looking at a cost of at least $1,400, mainly in parts.

Buy Here: S4 B9 Control Arm Parts

DIY Difficulty: Difficult

Audi B9 S4 Engine Reliability

Given that this vehicle is relatively new, (2017 – present), there isn’t much information on how long these can last. However, just like many other cars, if you keep up with the maintenance schedules religiously, you’ll be very satisfied with the reliability of the B9 S4. Scrolling through forums, we’ve seen some last as long as 150,000 miles.

When it comes to the S4, the S5 is a common comparison. Therefore, we’ve broke it down for you in our S4 vs S5 article.

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