Audi A4 B9
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The 6 Most Common Audi A4 B9 Engine 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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The A4 B9 is the fifth-generation, and latest, A4 released by Audi, and it is the successor to the A4 B8. The B9 A4 was revealed in 2015 at the Frankfurt Motor Show and was produced in 2016, in Europe, and 2017, in the US. The new B9 is wider, lower, longer, and lighter than the B8 and features a much-improved interior, and is built on Volkswagen’s MLB Evo platform.

Audi A4 B9 Engines

The Audi A4 B9 featured many engines out of the gate, 3 gas engines and 4 diesel engines. For the gas engines, there is a 35 TFSI (1.4TFSI/2.0TFSI) that puts down 148hp and 184lb-ft of torque, 40 TFSI (2.0TFSI Ultra) that puts down 187hp and 263lb-ft, and a 45TFSI (2.0TFSI) that puts down 249hp and 273lb-ft of torque. The 40 TFSI and 45TFSI each have quattro® versions as well. For the diesel engines, there is a 30 TDI (2.0TDI) the puts down 134hp and 236lb-ft of torque, 35 TDI (2.0TDFI) that puts down as much power as the 30 TDI with minor engine differences, 40 TDI (2.0TDI Ultra) that puts down 187hp and 295lb-ft of torque, and finally a 45 TDI (3.0TDI V6) that puts down 215hp and 369lb-ft of torque. The 40 TDI and 45 TDI each have quattro® versions available.

Before jumping into the common problems, we’ll be writing predominantly about the 2.0 TFSI engine and will be putting replacement parts for the 2.0 TFSI. So, if you are looking for parts or guides for a different engine, reach out in the comments and we’ll assist in any way possible.

Common Audi A4 B9 Engine Problems

  • Thermostat Housing Leaks
  • Premature Water Pump Failure
  • PCV Valve Failure
  • Leaking Engine Mounts
  • Premature Control Arm Failure
  • Faulty Power Window Regulator

1. Thermostat Housing Leaks

The thermostat housing on the Audi A4 B9 is made out of plastic, which is prone to premature failure. The thermostat is a crucial component in the cooling system of an engine. A thermostat regulates the coolant that is recycled back into the engine and how much coolant is chilled by the radiator before being recirculated.

If the thermostat fails or leaks, not only will the engine lose the coolant that it needs to run optimally, the engine will overheat. The main reasons a thermostat fails are normal wear and tear, a defective part, or not maintaining proper coolant levels. A thermostat, especially on Audi and Volkswagen’s, is not the most reliable part due to the plastic parts they are made out of. Usually, you will go through at least one thermostat throughout the vehicle’s life cycle.

Symptoms of Thermostat Housing Leaks:

  • High temperature on the temperature gauge
  • Low coolant indicator illuminating
  • Engine overheating
  • Erratic temperature readings
  • Improper coolant flow

Thermostat Housing Replacement Options:

When it comes to replacing the thermostat housing, we highly suggest replacing both the water pump and thermostat at the same time. Not only is it easier to replace both, but it’s also more cost-efficient. Replacing the thermostat housing and water pump is not a difficult DIY, but if you were to go to a mechanic, you should expect to pay around $1,000.

Buy Here: B9 A4 Replacement Thermostat
DIY Difficulty:

2. Premature Water Pump Failure

Just like thermostats in the A4 B9, the water pump is prone to premature failure. A water pump maintains the flow of coolant from the radiator to the engine and back to the radiator. Just like when the thermostat fails, the engine will overheat and lose coolant. If this goes ignored, major engine damage could occur.

The main reasons a water pump fails are pretty much the same for the thermostat: normal wear and tear, lack of coolant, or defective parts out of the factory. You will more than likely go through at least one water pump throughout the life cycle of the vehicle.

Symptoms of Water Pump Failure:

  • Engine overheating
  • Whining noises coming from the engine
  • Engine coolant leaks
  • Corroded part

Water Pump Replacement Options: 

As said above, we highly advise replacing both the water pump and thermostat while doing this repair. A mechanic or dealer charges around $1,250 to replace the water pump.

Buy Here: B9 A4 Replacement Water Pump
DIY Difficulty:

3. PCV Valve Failure

PCV valves, or sometimes called engine oil separator, are common to fail in many Audi and Volkswagen engines. A PCV valve is an important part of an engine because it essentially controls emissions that the vehicle gives off into the environment. It takes the gases produced by the engine’s crankcase and sends those gasses back into the combustion chamber to be burned. This prevents the engine’s crankcase from developing engine sludge.

If a PCV valve fails, the engine’s AFR will be thrown off causing the symptoms listed below. The main reasons these fail are normal wear and tear and being stuck in the closed or open position. You will more than likely go through these at least once in the vehicle’s lifecycle. A general rule of thumb would be to check the valve out every 60,000 miles/

Symptoms of PCV Valve Failure:

  • Rough engine performance
  • Rough idle
  • Engine misfires
  • Whistling noise coming from under the hood
  • Lean running conditions with P0171 or P0507 fault codes

PCV Valve Replacement Options:

The PCV Valve is not a hard DIY, nor is the replacement part too expensive, so we would advise doing it on your own to save on labor costs. However, not everybody is DIY savvy, so if you do plan on taking it to the shop, expect to pay around $700.

Buy Here: B9 A4 Replacement PCV Valve
DIY Difficulty:

4. Premature Control Arm Bushing Failure

Control arm bushings are not too common on these vehicles but are popular enough to include on this list. Control arm bushings are found in between a control arm and the subframe, so it helps distribute the road’s force and absorbs vibration making the drive more smooth.

If the bushings fail, you’ll be able to tell because the driving experience will not be near as smooth and you’ll notice the symptoms below. The main reasons for failure are due to normal wear and tear or being defective. Typically, control arm bushings should last the lifecycle of a vehicle.

Symptoms of Control Arm Bushing Failure:

  • Clunking noise from the transmission
  • Suspension squeaking over bumps
  • Rough driving experience
  • Steering wheel wandering
  • Vibration from the transmission
  • Un-even tire wear

Control Arm Bushing Replacement Options:

Control arm bushings are harder to replace if you don’t have the proper tools, (a car jack, etc). We would also advise replacing all of the bushings because they were not the best quality out of the factory. So needless to say, we would maybe even go with aftermarket bushings so you won’t have to worry about replacing the defective OEM ones. A mechanic would charge about $700 to replace the control arm bushings.

DIY Difficulty: Difficult

5. Leaking Engine Mounts

Engine mounts, also referred to as motor mounts, are not too common to fail, but again we’ve seen customers write about these leaking hydraulic fluid and wanted to make sure to include them on the list. This problem is more common on the Audi 4.0T engines. Engine mounts are, as it sounds, components that hold the engine in place and dampen or isolate any engine vibrations while driving.

If the motor mounts fail, you will be able to see hydraulic fluid leaking out of them and the driving experience will be rough since the engine won’t be held in place optimally. If ignored, this obviously can cause major damage to the engine. Again, these aren’t too common to failure and shouldn’t fail in the vehicle’s lifecycle, but many customers were writing reviews on these for the Audi A4 B9.

Symptoms of Leaking Engine Mounts:

  • Low hydraulic fluid
  • Excessive engine vibration
  • Engine impact noises from the engine bay
  • Engine misalignment
  • A rocky start

Engine Mount Replacement Options:

The longitudinal design of the 2.0 engines in the Audi A4 B9’s makes changing the engine mounts difficult. However, if you know your way around the engine, it could save a lot of money on labor. There are two options when it comes to replacing engine mounts: replace them with the OEM mounts or with aftermarket mounts. We would suggest aftermarket mounts to ensure higher quality in the mounts. A dealer or mechanic would charge around $1,000+ depending on the labor rates.

DIY Difficulty: Difficult

6. Faulty Power Window Regulator

There have been many faulty power window regulators in past Audis’s and Volkswagen’s and it sounds like the A4 B9 may have this issue as well. Power window regulators hold the window glass in two channels and makes the window go up and down.

As you can imagine, if a power window regulator fails, the power window won’t go up or down or could experience some of the symptoms listed below. Through a vehicle’s lifecycle, these shouldn’t fail.

Power Window Regulator Replacement Options:

  • Slower or faster than normal window speed
  • Clicking from the window switch
  • Power window stuck
  • Power window doesn’t stay up or is crooked
  • Multiple presses on the window switch to get the window up or down

Power Window Regulator Replacement Options:

Replacing the power window regulator is not hard, it’s just a tedious DIY. There are many DIYs out there that are easy to follow for this repair. When the power window regulator goes out, the only option is to change the regulator out. A local mechanic or dealer would charge around $400.

Buy Here: B9 A4 Replacement Power Window Regulator
DIY Difficulty: Intermediate

Audi A4 B9 Reliability

It seems to be that Audi has got the best A4 on their hands from a reliability standpoint. The Audi A4 B9 scored 5 out of 5 in Consumer Reports Overall Reliability score. In fact, Consumer Reports actually recommends the Audi A4 B9. This is mainly due to the 2.0TFSI engine being largely improved since its inception. There may seem like a lot of problems listed above, but these are what we have found so far. Not all of them are super common, but we think it is important to point out problems consumers have seen so far. After all, the Audi A4 B9 is only 4 years old.

As with any newer car, we would advise going with the later model years (2019+), just because it allows Audi to work out the kinks seen in the younger years. If you are driving an A4 B9, let us know what problems you have encountered in the comments. As always, if you want to read more Audi content, here is our write-up on The 7 Most Common B7 Audi A4 Engine Problems.

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  1. My 2017 A4 with the 45 TFSI engine had a motor mount failure but luckily it was covered under certified pre-owned warranty at 40k miles. Car has 45k miles now and dealer now says its out of warranty and a recent door sub woofer failure (seems its a known issue) will not be covered. The battery appears to be on its way out as well. I have taken good care of this car since I got it with 9,000 miles. All services were done at Audi. I will take care of whatever I can do myself but if I encounter myriad problems going forward, I will never buy another Audi product.

    1. Update: the water pump and thermostat had to be replaced since the plastic part sprung a leak before 45k miles. I am definitely not considering another Audi in the future,

  2. Well I have had two of the problems mentioned..I.e water pump/ thermostat failure and front upper control arm bushes failure.. one on either side…water pump was done by an Audi specialist and the control arms I’m going to do myself…removing the pinch bolt.s the most difficult part apparently….plenty of penetrating oil before hand!
    keeping a close eye on the other problems mentioned.
    I would add I have also have had a leaky transmission mount fail…not expensive and easily doable myself.
    2017 Audi A4 Avant s line 2.0t

  3. A new issue now in December is slight vibration seemingly coming from a misfire. Car has 47,000 miles and since spark plugs were replaced at 40k miles I suspect it could be the pcv valve…

  4. Had water pump leak dealer replaced it car has 45 000km, now I have worn left engine mount at 75 ooo km. other than that car has been totally amazing and still loving it. mine is 2016 Audi A4 2.0tfsi B9, thank so much for this website

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