C7 Audi S6 Ultimate Guide

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The C7 Audi S6 was first introduced in 2012 and continued production through 2018. It is the fourth generation S6 and it was built on the Volkswagen Group’s C7 platform. The S6 is positioned between the A6 and RS6. The C7 is a much more modernized S6 than its predecessor. It has updated headlights, tail lights, and sleeker/sharper body edges. It went through a facelift in 2015, sometimes referred to as the C7.5 S6. This facelift included updated headlights and interior technological upgrades. There are two body styles that the S6 is available in a 4-door sedan and a 5-door Avant. The 5-door Avant is much harder to find.

The C7 Audi S6 features an EA824 4.0T, or 4.0tt, V8 Biturbo (twin-turbo) engine that puts out 414hp (309 kW) and 406 lb-ft (550 Nm) of torque. This engine was later upgraded in 2015 with the facelift to 444 hp (331 kW). We’ll touch more on engine performance in the “performance” section below.

C7 Audi S6 Specs

In this section, we will be going over some interior and exterior specs for the 2023 four-door sedan and the five-door Avant.

A new C7 S6 Avant is hard to come by, but there are some out there. There’s also the RS6 Avant, which happens to be one of our favorite Audi’s out there.

C7 Audi S6 Pricing

In this portion, we’ll be covering new and used prices for the C7 Audi S6. For new prices, a 2023 S6 Premium sedan starts at $72,700, a Premium Plus S6 sedan starts at $77,400, and, lastly, a Prestige S6 sedan starts at $81,500. If you are looking for the Avant version, you will likely have to look for a new RS6 Avant, which is much more expensive than a regular S6. However, the RS6 Avant only has one trim and it starts at $116,500. Now on the used side, depending on what year and mileage, an Audi C7 S6 can range anywhere from $15,199 – $58,989. If you are confused about Audi trims, here is a little write-up on the different Audi trims.

The 6 Most Common C7 Audi S6 Engine Problems

1. Ignition coil or spark plug failure
2. Turbo oil supply line filter clogged
3. Premature thermostat and/or water pump failure
4. PCV valve/engine oil separator failure
5. Coolant pipe leaking on turbocharger
6. Premature active motor mount failure

1. Ignition Coil Pack and Spark Plug Failure

Premature ignition coil and spark plug failure are common in many modern engines nowadays. Ignition coils turn the battery’s low voltage into the high voltage the spark plugs need. Once the spark plugs obtain this voltage, they create a spark in the combustion chamber starting the combustion process. Needless to say, ignition coils and spark plugs are crucial ignition components. There is one ignition coil and one spark plug per cylinder. Therefore, the 4.0T V8 engine has 8 ignition coils and 8 spark plugs.

There are a couple of reasons these ignition components can go bad: normal wear and tear or pushing the engine past its optimal engine conditions. The spark plug maintenance intervals for the 4.0T engine is 35,000 miles or every 6 years, whichever comes first. Then, 40,000 miles after the first set change.

Symptoms of Ignition Coil or Coil Pack Failure:

• Check Engine Light (CEL) or Malfunction Indicator Light (MIL) illuminating
• Cylinder misfires with P0300 – P0308 fault codes present
• Rough idle
• Poor engine performance
• Difficulty turning the engine on

Ignition Coil Replacement Options:

When it comes to replacing ignition components, there are only two options: replace them with high-performance components (1-step colder spark plugs) or replace them with OEM components. Although more expensive, we advise replacing both the coils and spark plugs all at once to avoid near-future misfires. To replace ignition coils and spark plugs in a 4.0T, you’ll be looking at a bill of ~$1,200. If you happen to know your way around the engine, DIYing this replacement would be very cost-effective.

Audi S6 C7 OEM Ignition Coils
Audi S6 C7 OEM Spark Plugs

DIY Difficulty: Intermediate

2. Turbo Oil Supply Line Filter Clogged

This is the issue where the 4.0tt gets a bad reputation because it can cause the turbochargers to blow. The purpose of a turbo oil filter is, as it sounds, to filter oil before going into the turbocharger to ensure clean and filtered oil is going into the turbocharger. Out of the factory, these filters were failing, or prematurely clogging, which was causing the turbos to be oil deprived and blow. Audi has addressed this issue in this TSB 21 18 30 2044640/5.

Symptoms of a Clogged Turbo Oil Supply Line Filter:

• Blown turbochargers
• Engine stalls
• Engine sputters
• Reduced engine performance
• Low oil pressure

Turbo Oil Supply Line Filter Replacement Options:

There have been many updates to the filters over the years and this shouldn’t be an issue now. However, if you are in the market for a used C7 S6, make sure the filters have been addressed before purchasing. If you are wanting to perform preventative maintenance on the filters, a shop would likely charge around $750 to replace them. As anyone can imagine, if the turbos fail, they can get very expensive to repair.

DIY Difficulty: Intermediate

3. Premature Thermostat and/or Water Pump Failure

Water pump and thermostat failure are common in many Audi engines, not excluding the Audi 4.0tt. A water pump maintains the flow of coolant from the radiator to the engine block, while a thermostat regulates the amount of coolant that is cooled by the radiator before being recycled and how much coolant is recycled back into the engine. Both of these components are crucial in an engine’s cooling system. Without one or the other functioning, an engine can overheat very quickly.

In most 4.0tt’s, the thermostat would be the issue. However, this doesn’t mean that the water pump can’t fail. In these engines specifically, Audi issued a TSB 19J1 which speaks to the faulty thermostat. Typically a water pump or thermostat should last up to 80,000 miles under optimal engine conditions.

Symptoms of Premature Thermostat and/or Water Pump Failure:

• Low engine coolant/antifreeze indicator illuminating (more often than normal)
• Engine overheating
• Limp mode engaged
• Coolant leaking under the car
• Sweet smell in the engine bay
• Erratic temperature readings

Thermostat and/or Water Pump Replacement Options:

When a water pump or thermostat starts to fail, the only choice is to replace them. Both the water pump and thermostat are relatively inexpensive, compared to other parts. Although an intermediate DIY service, this would save a ton on labor costs. If you were looking to take your C7 S6 to the shop for this service, look to spend around $800 for the thermostat alone.

4.0T Thermostat Replacement

DIY Difficulty: Intermediate

4. PCV Valve/Engine Oil Separator Failure

Another common VW or Audi failure is the PCV valve. In some Audi’s this may be referred to as the engine oil separator. The engine oil separator removes excess fumes from the oil before it goes into the combustion chamber. If this valve happens to fail, AFR conditions will be thrown off and would mostly be on the lean side. Most of the time, a PCV valve fails because it is stuck in the open or closed position. This part is prone to fail at least once in a vehicle’s life cycle. It should be inspected at least every 60,000 miles.

Symptoms of PCV Valve/Engine Oil Separator Failure:

• Rough idle
• Engine misfires
• Whistling noise coming from the engine
• Lean AFR conditions

PCV Valve/Engine Oil Separator Replacement Options:

If the engine oil separator does happen to go bad or get stuck, the only way to fix it is to replace it. The part is relatively inexpensive and this is one of the easier DIYs on the list. If you aren’t comfortable with the DIY, a shop will likely charge around $600 all in.

4.0T PCV Valve/Engine Oil Separator Replacement

DIY Difficulty: Easy

5. Coolant Pipe Leaking on Turbocharger

What seems to be a common problem that isn’t documented much is the coolant pipes leaking onto the turbocharger. This would lead to many owners smelling coolant under the hood but not being able to find the leak. Two coolant pipes go directly into the turbos: the coolant feed pipe and the coolant return pipe. These specific pipes bring coolant in and out of the turbocharger. The pipe that causes the most issues is the coolant return pipe.

So many owners started to complain about this, so Audi made a TSB#2036167/1 outlining the issue and solutions. Coolant pipes, especially if made out of metal, should last the lifecycle of a vehicle.

Symptoms of Coolant Pipe Leaking:

• Low coolant indicator illuminating
• Low coolant level in the reservoir
• Black crust or buildup on the turbo coolant lines
• Sweet coolant smell emits from under the hood

Coolant Pipe Replacement Options:

If you happen to see black crust on the coolant lines, make sure to act on it as soon as possible. Although this causes slow coolant loss, it could lead to issues down the road if ignored. If the C7 S6 is under warranty, Audi should fix it at no cost. However, if not under warranty, expect to pay around $750 – $1,000.

DIY Difficulty: Difficult

6. Premature Active Motor Mount Failure

Active motor mounts were new technology when the 4.0tt engine came out. Unfortunately, it was common for them to fail in 2013 & 2014 C7 S6s. Active motor mounts are designed to optimally dampen and isolate engine vibrations and noises for a smoother driving experience. The main reasons these would fail are being faulty out of the factory or normal wear and tear. Customers were reporting heavy engine vibrations and noises from the engine banging around the engine bay. This forced Audi to issue a TSB 27 14 22 2036392/2. In essence, Audi updated the active motor mount parts to be more reliable.

Symptoms of Active Motor Mount Failure:

• Heavy engine vibrations
• Engine misalignment in the engine bay
• Impact engine noises – banging, clanking, etc
• Rocky startup on startup
• Engine movement

Active Motor Mount Replacement Options:

When active motor mounts fail, there are only two options: replace them with OEM mounts or replace them with aftermarket mounts. The aftermarket mounts are cheaper and tend to have a good reputation. This is not an easy DIY, but could be done in a day’s work with the proper tools. A shop would likely charge ~$1,000 for this service.

4.0T OEM Active Motor Mount Replacement

DIY Difficulty: Intermediate

C7 Audi S6 Mods

Now that the common problems have been covered, we can jump into the fun part, mods. These beast V8 engines have a lot of potential when it comes to modding them, especially with twin-turbos. We’ve seen many C7 S6 owners posting 10-second 1/4 mile times. The 5 mods listed below are a great starting point for someone looking to push up to 600hp!

1. ECU Tune
2. DSG/TCU Tune
3. Air Intake
4. Downpipes
5. Upgraded Turbo Outlet Hoses

The only issue once you go to Stage 2 is that the clutch tends to fail because the factory clutch can’t sustain such increased power over stock.

C7 Audi S6 Reliability

Unfortunately, when it comes to the reliability of the C7 S6, there isn’t much data to go on other than forums. Therefore, what we’ve gathered is that the C7 S6 is pretty reliable but expensive to maintain. However, this shouldn’t come as a surprise. Anyone in the market for a luxury vehicle should know the costs that come with it. The 2013 model year is deemed to be the least reliable, mainly because it was the first production year of the C7 S6. The C7.5 S6 (2016-2018) tends to be the most reliable because it has given Audi many years to tweak all of the issues/problems in previous model years. There is one issue that tends to give the 4.0T engine a bad rep and that is turbo failure. However, this is hit or miss, so with proper maintenance, the C7 S6 is pretty reliable.