Article Updated: January 24, 2023
The B8 S4 was launched in late-2008 with the all-new 3.0L TFSI Supercharged V6. It used an Eaton supercharger which sat inbetween the “Vee” of the block, and was cooled with two separated water-to-air intercoolers. At 329hp and 325lbft of torque, it nearly matched the performance numbers of its predecessor, the B7, but with only 6 cylinders and a significantly smaller engine.
In early 2012, it received a facelift which included both appearance and technical upgrades. Post-facelift models are known as B8.5’s as the upgrades were significant enough to require a distinct separation of the two cars by the Audi community. Before we jump into problems with this vehicle specifically, let’s discuss how the B8.5 compares to the B8 in terms of reliability.
Check here for the most common problems on the B8 A4.
Audi B8 vs. B8.5 Reliability
The general consensus is that the B8.5 S4’s are significantly more reliable than the B8 S4’s. One of the main problem areas of the B8 models was the DSG or “S-Tronic” transmissions. The transmissions had issues with the mechatronics, caused by design defects. These problems were fixed in 2012 with the new Gen II DSG transmission that was included in the B8.5 models.
On B8.5 models, there aren’t any huge failure points that you can expect, outside of the normal issues that most Audi’s face such as the coils packs. Unfortunately, that can’t be said for the B8 generations, as the transmission continues, to this day, to be a high-failure point for S4’s that have not replaced their expensive mechatronic units with defect-free versions. Outside of this, the B8’s are prone to the same water pumps, thermostats, coil packs, etc. The water pump was upgraded in late 2010 or 2011 which reduced the commonality of failure.
Overall, the transmission problems and water pump problems in earlier year B8’s make the B8.5 more reliable and less problematic.
Audi B8 S4 Common Engine Problems
- DSG / S-Tronic Transmission
- Water Pump Failure
- PCV Valve / Excess Oil Burn
- Carbon build-up
- Misfires: injectors, coils packs, and spark plugs
1. B8 S4 DSG/S-Tronic Transmission Failure
It’s been estimated that possibly near 20% of all B8 S4’s suffered problems with their DSG transmissions. The most prevalent problems occurred with the Mechatronics unit failing and requiring replacement – a job that costs at least $4k to fix. The mechatronics unit that controls shifting is located within the oil-cooled system, creating circuit board issues. The oil reacting with the board, and heat from the oil would cause the unit to fail, resulting in jerky shifts from first to second gear, or vice versa.
The mechatronics unit is most likely to go out above the 20k mile range. However, in today’s time, it’s likely hard to find a B8 S4 with less than 20k miles, so I’d check to make sure this problem has been fixed prior to purchasing a pre-2012 B8. In 2012, along with the B8.5 facelift, Audi upgraded the transmission to the “Gen II” DSG transmission, which fixed the mechatronics failure issues.
Outside of the mechatronics unit, the gear change sensor was prone to failure, which can lead to a “Gearbox Malfunction – You Can Keep Driving” message. Additionally, the clutch pack could fail prematurely, although this problem appears to be significantly less common.
2. B8 S4 Water Pump Failure
Audi’s are known for their excessive water pump problems. Don’t worry, it’s just as much of a problem on BMWs. This vehicle is prone to premature and excessive water pump failure.
The water pumps use an impeller which is responsible for pumping the fluids through the water pump and through the cooling system. The impellers were unintelligently made out of plastic, which makes them very susceptible to failure over time as they operate in a highly pressurized environment. When the impeller breaks or fails, the water pump loses all of its pumping powers and is no longer able to push coolant through the cooling system. The end result: your engine overheating and your car being stuck on the side of the highway, waiting for a tow truck. The OEM water pump is known to fail every 50k-80k miles.
Aside from the water pump, the B8 S4’s are also prone to thermostat failure. The thermostats commonly get stuck in the closed position, which prevents coolant from flowing through the engine, leading to overheating.
Water Pump Failure Symptoms
- Engine overheating
- Low engine coolant
- Smoke coming from the engine bay
- Coolant leaking from the engine bay
- Check engine light, codes: P3081, P2181, P0087, P00B7, etc.
Water Pump/Thermostat Replacement Options:
The easiest replacement option is upgrading to a water pump with a metal impeller. If you continually replace it with an OEM pump, you can expect it to continue failing. Water pumps with metal impeller issues mitigate all problems caused by the plastic impellers, creating more reliable water pumps. It would be advised to replace the old unit with the kit linked below because it includes an upgraded metal impeller water pump, upgraded thermostat, gaskets, and o-rings. If you are keen to DIYs, this is an intermediate job, but there are many videos online that go over it step by step. However, if you would rather take it to a shop, the bill would likely be around $350 – $500.
Buy Here: Replacement B8 S4 Water Pump Kit (Fits Up to 2012 Model Year)
DIY Difficulty: Intermediate
3. B8 S4 PCV Valve Failure
The PCV valve is the “positive crankcase ventilation” valve. Engines naturally make hazardous gases that are bad for the environment. The PCV valve’s job is to re-capture these gases and then send them back through the combustion chamber for them to be further burned down. In addition to being bad for the environment, these gases are also bad for your engine, resulting in carbon buildup and other “sludge” building up in the engine.
A failing PCV valve can lead to performance issues. Some common problems created by a bad PCV valve are misfires, excessive oil consumption, poor AFR’s, and oil leaks. One of the most tell-tale signs of a bad PCV valve is excessive oil consumption. Most owners report guzzling 1 liter of oil every 1,500 to 2,000 miles. Also, some owners have reported oil and coolant mixing if the PCV starts to fail. Therefore, if this is the case, you will want to act relatively quickly and replace it.
Failing PCV Valve Symptoms
- Rough idling, misfires
- Whining noise coming from the engine on acceleration
- Lean AFR’s (air to fuel ratios)
- P0171 and P0507 engine fault codes
PCV Valve Replacement Options:
When it comes to repairing the PCV valve, there’s really only one option and that is to replace it with a new one. The product linked below is just the PCV valve, however, we would advise getting the whole kit to ensure all gaskets and o-rings are fresh as well. If you are wanting to DIY this service, there are many videos online that you can follow step by step, and it also isn’t the easiest job to perform. A shop will likely charge over $1,000, mainly due to labor costs. We’ve seen quotes anywhere from 5 – 8 hours to complete this service.
Buy Here: Replacement B8 S4 PCV Valve (Fits Up to 2012 Model Year)
DIY Difficulty: Intermediate
4. Carbon Buildup
Like all modern Audi’s, the S4 uses direct injection. Audi likes to call it “stratified injection”, hence the TSI, FSI, and TFSI monikers. Direct injection systems inject the fuel directly into the cylinders, unlike port-injection systems which inject the fuel into the intake valves. Gasoline is sprayed into the engine at very high pressures. So, in a port-injection engine, you have highly pressurized gas going through the intake valves, which ultimately cleans and clears the valves of all gunk or build-up inside of them.
On direct injection engines, the gasoline is sprayed directly into the cylinders, bypassing the intake valves. Therefore, the intake valves are prone to carbon build-up which is gunk or sludge that builds up in the intake valves. Excessive carbon build-up can lead to performance problems as it restricts airflow and reduces volumetric capacity. Additionally, it can impact engine idling and cause rough idling, stuttering, dreaded misfires, etc.
Carbon Buildup Symptoms
- Decreased performance and driveability
- Poor idling, engine stuttering, etc.
Unless you have an extremely high mileage S4, you probably won’t notice the carbon buildup or the performance decrease until you clean the intake valves. The best method for doing this is through walnut blasting the intake valves. We recommend a walnut blast every 50,000 miles to keep your engine running in tip-top shape.
5. Bad Injectors, Coil Packs, and Spark Plugs
Another frequent problem on S4’s is misfires. Misfires can be caused by dozens of part failures, but the most common is bad injectors or bad coil packs. On the S4, coil packs tend to be more problematic than the injectors.
Coil packs are responsible for delivering electricity to the spark plugs, which gives them their spark and allows them to create combustion. When coil packs fail, they usually fail one at a time, creating cylinder-specific misfires. When a coil fails, the spark plug gets no power, which prevents the cylinder from igniting. This can cause fuel to build up in the cylinder, which can then pre-detonate off-time from heat. Additionally, it can cause the cylinder to not detonate at all.
Coil packs usually go bad every 40,000 to 50,000 miles on the S4. Replacing them is a simple DIY.
Coil Pack Failure Symptoms:
- Cylinder misfires
- Misfire codes (P0300 to P0306)
- Slow engine starting
- Rough idling, poor acceleration, stuttering, etc.
Coil Pack Replacement Options:
If one coil pack fails, odds are the others aren’t close behind. We always advise replacing the coils and plugs all at once to ensure fresh ignition components are being used. This replacement service is pretty simple and shouldn’t take any longer than an hour or two. A shop will likely charge about $400 to replace all of the ignition components, coils and plugs.
B8 S4 Common Problems Conclusion
Outside of the DSG transmission failure, the common problems listed above are relatively common across all Audi’s. Compared to the B8.5 models, the water pumps fail more frequently and the B8.5 doesn’t have transmission problems as they were fixed with the facelift in 2012.
Due to the DSG transmission problems being so common, the B8 S4 is considered somewhat unreliable and expensive to own. If you are looking at an S4, choosing one made after 2012 will result in fewer problems. Additionally, smaller problems tend to get fixed over time by manufacturers, such as the water pump issues, so later model S4’s are going to be more reliable than earlier model ones. The B8.5 S4’s are considered reliable and are great daily drivers or performance platforms for further modification.