Audi’s 4.0t V8 twin-turbo, commonly referred to as 4.0tt, was first introduced in 2012 in the Audi S6, S7, and S8. It’s a 90-degree V-angle V8 engine that produced 520hp and 479lb-ft torque to the crank. It was not only featured in many Audi vehicles, but was also featured in many Porsche’s, Bentley’s, and Lamborghini’s.
This innovative engine featured an all-new cylinder on demand system that when the engine operates on part load, four of its cylinders are deactivated. This innovation lowered fuel consumption by 5% and also reduced emissions substantially. The 4.0 TFSI v8 was awarded the Digital Trends Engine of the Year.
Audi’s that use the 4.0T
- 2012-2018 Audi C7 S6
- 2012-2017 Audi S7
- 2012-2018 Audi D4 A8
- 2017-Present Audi D5 A8
- 2012-2020 Audi D4 S8
- 2013 – 2019 Audi RS7
- 2013 – 2018 Audi C7 RS6
Something worth mentioning before getting into the common problems of this engine is, please make sure the replacement parts fit your vehicle before ordering.
Audi 4.0T Engine Problems
- Ignition Coil Failure
- Turbo Oil Supply Line Filter Clogged
- Motor Mounts Failure
- PCV Valve/Engine Oil Separator Failure
- Thermostat Failure
1. Ignition Coil Pack and Spark Plug Failure
Ignition coils and spark plugs are very common to go out in many Audi’s. The Ignition coils transform the voltage from the battery to a higher voltage for the spark plugs to create a spark and create combustion. The main reason either of these seem to fail is by normal wear and tear or by pushing an engine past its optimal engine conditions.
A good rule of thumb is to change both the spark plugs in the first 35,000 miles, and 40,000 miles thereafter. Whenever an ignition coil goes out, it is best to replace all 8. It may be expensive, but it will be worth it in the end.
Symptoms of Coil Packs/Spark Plugs Failure:
- Check Engine Light (CEL) illuminating
- Engine misfires
- Rough idle
- Loss of engine performance
- Engine not turning over
Coil Pack/Spark Plug Replacement Options:
When it comes to ignition coils and spark plugs, it is important to replace them all at the same time to give the vehicle a fresh set. If you plan on DIYing this, make sure you have the proper tools and it’ll be a rather easy DIY. If you aren’t looking to DIY and are wanting to take it to a shop, you would be looking at a cost of around ~$1,200 mainly due to the cost of parts.
2. Audi 4.0t Turbo Oil Supply Line Filter Clogged
This is a very common problem when it comes to the Audi 4.0tt and has caused many blown turbochargers. There are many names for this, but pretty much the role of the turbo oil filter is to filter oil before entering the turbocharger to ensure clean oil is going into the turbos. The filters were failing out of the factory because they were getting clogged too quickly and not enough oil was getting to the turbos.
This problem was so common that Audi has addressed the filter with TSB 21 18 30 2044640/5. There have been many updates to the filter by Audi because they realize the issues it was causing. If you have or are looking at an Audi 4.0t engine, make sure this has been replaced or you will be looking at an expensive repair.
Symptoms of Turbo Oil Filter Clogged:
- Blown turbochargers
- Engine stalls
- Engine sputters
- Reduced engine performance
- Low oil pressure
Turbo Oil Supply Line Filter Replacement Options:
If the turbo oil supply filters haven’t been changed on an Audi 4.0tt you are looking at or currently own, replace them ASAP. This DIY is not the easiest because the filters themselves are not very easy to get to, but if you know your way around the engine, you should be able to get it done. If you are looking to take the vehicle into the shop, you would be looking at a cost of ~$750 mainly due to the cost of labor.
Turbo Oil Supply Line Filter Replacement: https://audi.us/3kNxFML
DIY Difficulty: Intermediate
Video DIY Guide: https://www.youtube.com/watch?v=8QqRPCeIvAA
3. Audi 4.0t Active Motor Mounts Failure
Another common 4.0t engine problem was the active motor mounts failing. Active motor mounts were new technology in the Audi 4.0t when they first came out. The purpose of active mounts is to optimally dampen and isolate engine vibrations and noises to ensure a smooth ride.
This problem was also very common that Audi issued another TSB 27 14 22 2036392/2 to address this issue in all 4.0t engines. There are two ways that these can fail: they are either the faulty mounts out of the factory or normal wear and tear have caused them to go bad. Again, if you are looking to own a 4.0t or currently own one, make sure these have been updated to the latest revisions that Audi released.
Symptoms of Active Motor Mount Failure:
- Heavy engine vibrations
- Impact engine noises – banging, clanking, etc
- Engine movement
Active Motor Mount Replacement Options:
There are really two options when it comes to active motor mount failure: replace them with the OEM parts or replace them with the aftermarket part. The aftermarket part is cheaper but has some other improvements over the OEM part. It certainly is not the easiest DIY, but it can be done in a day’s work. This service at a shop can run up a bill of ~$1,000.
OEM Active Motor Mount Replacement: https://www.ecstuning.com/Audi-C7_S6-Quattro-4.0T/Engine/Mount/
Aftermarket Active Motor Mount Replacement: https://bit.ly/3yBiRpn
4. PCV Valve/Engine Oil Separator Failure
PCV valve or engine oil separators are common to not be very reliable out of the factory from Audi’s or Volkswagen’s. These remove excess gases from the oil before the oil goes into the combustion chamber. If they fail, the engine AFR will be thrown off causing the symptoms listed below.
This part is prone to fail at least once in the vehicle’s lifetime and should be looked at every 60,000 miles. The two main reasons this part fails are: normal wear and tear or by being stuck open or closed.
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 an engine oil separator does happen to fail, the best fix is to just replace it with a new one. The replacement part isn’t very expensive and the DIY is pretty straightforward. A shop will charge you about ~$600 split between parts and labor.
PCV Valve/Engine Oil Separator Replacement: https://audi.us/2Vfg8Va
DIY Difficulty: Easy
Video DIY Guide: https://www.youtube.com/watch?v=Ss0BaygixHw
5. Thermostat Failure
Thermostat failure is also another common problem seen in many Volkswagen’s and Audi’s engines. A thermostat is crucial in a vehicle’s cooling system. It regulates the amount of coolant that is sent back to the engine and how much is cooled in the radiator before going back to the engine. If a thermostat happens to fail, you will not be able to drive for long because the engine will be prone to overheating.
In 4.0t’s, this was common enough so Audi issued TSB 19J1 to address the problematic thermostat. If the thermostat has not been replaced under the TSB listed above, make sure to get it replaced ASAP. A normal working thermostat should last up to 70,000 miles.
Symptoms of Thermostat Failure:
- Engine overheating
- Low coolant levels
- Engine temperature being sporadic
- Whining noise coming from the engine
Thermostat Replacement Options:
When a thermostat goes out on a 4.0tt, the best thing to do is to just replace the entire unit. Again, like the engine oil separator, the parts are relatively cheap and the DIY is straightforward. If you are looking to take it to a shop to replace, you would be looking at a cost of around ~$800.
Thermostat Replacement: https://bit.ly/3BvgVR2
DIY Difficulty: Easy
Video DIY Guide:
Audi 4.0t Reliability
The Audi 4.0t engine’s reliability gets a bad rep because of the turbo oil supply line filter getting clogged and blowing turbos. Other than the 5% of cases with this issue, if that, the Audi 4.0t engine is pretty bulletproof IF maintenance schedules are followed. Something worth mentioning is that repairs and maintenance on this engine are not cheap, as expected. We wouldn’t expect this engine to last much longer than 120,000 miles without having to pay big bucks for repairs.
Also, if you want to check out more Audi content, here is our write-up on the common problems for a 4.2 V8.