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Audi’s B5 S4, or also called Audi S4 quattro, was the successor of the C4 S4, or the original Audi 100 S4, and it was the second generation S4 Audi produced. It debuted in 1997 on Volkswagen’s B5 platform, compared to the C4 platform 3 years prior, and was produced through 2002. It came in two different body styles: sedan & wagon (Avant). Shortly after its release, it became an enthusiast car because of how much power could be put into it without having to spend a fortune and was featured in the “Sport Compact Car” magazine in 2007.
Audi B5 S4 Engine
Under the hood, the B5 S4 featured a 2.7T (twin-turbo) V6 that put down 261hp and 295tq with AGB/APB/AZB engine codes. However, in the US market, to meet emission standards, the engine was detuned to outputs of 247hp and 258tq. BORING. It had two transmissions to choose from: a six-speed manual and an all-new five-speed Tiptronic automatic transmission. This engine gets mixed reviews from the Audi enthusiast community because some claim this is the best engine Audi has ever made to the worst. In this guide, we’ll be showing the common problems seen in this engine. Given its ability to put out extreme power numbers at a relatively low cost, we love this engine.
Common Audi B5 S4 Engine Problems
- Ignition coil pack failure
- Stock turbo failure
- Faulty torque converter
- Premature CV Boot/Joints Failure
- Cam tensioner failure
- Valve cover gasket failure
- Faulty coolant temperature sensor
1. Ignition Coil Pack Failure
If you have read any of our previous posts, you would know that ignition coil failure is very common in VW and Audi engines, especially in vehicles that have been modified. Ignition coils transform the battery’s low voltage into an incredibly high voltage that spark plugs need to create a spark initiating engine combustion. Without one functioning ignition coil, the vehicle will run rough, but with multiple ignition coils out, the engine may not even start.
There are two main reasons ignition coils fail: normal wear and tear (around 60,000 miles) or modified engines. Factory ignition coils are meant for factory engines. When it comes to modifying an engine, make sure to invest in better coils and colder spark plugs, linked below, to avoid engine misfires. An unmodified engine will typically go through at least two sets of ignition coils, while a modified engine, if not upgraded coils, could go through many more sets.
Symptoms of Coil Packs Failure:
- Check Engine Light or Malfunction Indicator Lamp illuminating
- Engine misfires with fault codes P0300 – P0306
- Sluggish engine performance
- Engine stalls or surges
- Difficulty turning over the engine
When it comes to replacing failing ignition coils, we highly advise replacing all of them at the same time because they generally go out around the same time and it will be less of a headache in the long term. With the proper tools, this is a pretty straightforward DIY. A local mechanic or dealer would likely charge around $150 for ignition coils, but $400 for coils and plugs.
2. Stock Turbo Failure
For some reason, the stock turbos commonly go out on the 2.7T engines. Turbochargers increase an engine’s power and torque by compressing more air flowing into an engine’s cylinders. Without a functioning turbocharger in a turbocharged engine, performance will take a huge hit and, if ignored for a long period of time, can cause major engine damage.
Now the 2.7T, as stated above, is a twin-turbo (biturbo) engine, and both of the turbos tend to go out at the same time. Turbos aren’t supposed to fail out of the factory, so why are these more common? There are many circumstances for turbos to blow: oil starvation, overspeeding, debris, heat, etc. But many have said the main reason for these K03 turbo’s failing is heat because of their location in the engine bay. They’re in between the engine block and firewall with a heatshield insulating everything. As you can imagine, that is a recipe for blown turbo’s.
Symptoms of Turbo Failure:
- Obvious power loss
- Loud whining noise from the engine bay
- Blueish grey smoke emitting from the exhaust
- CEL/MIL illuminating
When it comes to replacing blown turbo’s, it isn’t cheap. But you have two options: buy two more K03’s or upgrade to K04’s for a little more money, but a lot more power. If you aren’t trying to get more power, you might as well upgrade since they have to be replaced anyway. We wouldn’t recommend replacing turbo’s on your own unless you have the proper tools. On the 2.7T’s, the engine has to be fully removed to replace the turbo’s. For a service like this, a shop will likely charge $1,000 – $1,500 in labor.
3. Faulty Torque Converter
There are a handful of engines in Audi’s and VW’s that have faulty torque converters, often referred to as “TC”, so it isn’t too common but is apparent in automatic B5 S4’s. A torque converter essentially makes a vehicle move. It transmits the engine’s torque to a rotating driven load.
There are many reasons a torque converter can fail: slippage causing overheating, permanently locked, blade deformation or fragmentation, seals leaking etc. When it does fail, a check engine light will turn on and you may experience shuddering and slippage. This may not occur in all B5 S4’s, but you will likely go through at least one torque converter through the vehicle’s lifecycle.
Symptoms of Torque Converter Failure:
- CEL/MIL illuminating with fault code P0740 or P0741
- Slipping gears or not shifting at all
- Transmission overheating
- Transmission leaking fluid
- Metal scraping noise from the transmission
When replacing a faulty torque converter there are two main options: replace with an OEM unit or replace with an aftermarket unit. If you are someone trying to go for big power, we would advise upgrading the torque converter even if it hasn’t gone out. Given the TC is found in the transmission of the vehicle, it is not a very easy DIY. A mechanic would likely charge $1,800-$2,000 for parts and labor.
DIY Difficulty: Difficult
4. Premature CV Boot/Joints Failure
Another pretty common problem with Audi’s is premature failure of the CV (Constant Velocity) boots which leads to CV joint failure. A CV boot essentially encases the CV joint and lubricant to make sure the CV joint functions properly. A CV joint is found on the ends of the driveshaft, so its purpose is to connect the driveshaft to the transmission.
What will typically happen when CV boots fail, is they will tear, because they are made out of rubber, and leak the lubricant needed for the CV joints to function. Also, when they tear, this allows debris from the road to get into the boot and ruin the joints. When the CV joint fails, you’ll start to hear clicking while turning and possible steering wheel vibrations. If ignored, this could cause major damage to the axel. Although not TOO common, a vehicle COULD go through one set of CV boots and joints in its lifecycle.
Symptoms of CV Boot/Joint Failure:
- Cracks on the CV boots
- Rough vibrations from the axel
- Clicking/creeking noise while turning
- Wandering steering
- Steering wheel vibration while turning
We highly advise having the CV boots inspected every service visit for tears to avoid CV joint damage. If you can catch premature tears, you can avoid damaging the CV joints. Replacing the boots themselves is not too difficult, but the joints are a different story. It is possible to DIY if you have the proper tools, however, it will take a while. A mechanic will likely charge $500 to replace a CV joint. While you’re fixing the CV boots & joints, a popular thing to do is add some coilovers. We love a nice lowered B5 S4 with a nice set of coilovers.
5. Timing Belt Tensioner Failure
A very common problem with Audi’s and Volkswagen’s is tensioner failure, which leads to timing chains stretching or timing belts snapping. The components that the tensioners were made out of weren’t the most reliable. A tensioner does what it sounds like, maintains the proper tension for the timing belt to function optimally. If the tensioner happens to fail, worst case is the timing belt snaps causing major engine damage.
Since the tensioners components are the most reliable, they typically fail by cracking or wobbling. Since a timing belt typically lasts around 75,000 – 100,000 miles, it is advisable to replace the tensioners around that threshold as well. A vehicle shouldn’t go through more than two tensioners or belts in its lifecycle.
Symptoms of Timing Belt Tensioner Failure:
- CEL/MIL illuminating with P0016 or P1340 fault codes
- Rough engine performance
- Engine timing off
- Stretched timing belt
- Engine stalls
- Rattling or rumbling noise while changing gears
As stated above, when a tensioner goes out, we highly advise changing out the timing belt as well. There are two options when it comes to replacing tensioners and timing belt: change it out with OEM parts or aftermarket parts. We advise the aftermarket route, although it may be a little more expensive today, it will save you money in the long term. Changing belts and tensioners is extremely difficult, so unless you know what you’re doing, don’t do this DIY. A mechanic or local dealer would charge around $1,250.
6. Valve Cover Gasket Failure
Valve cover gaskets are not this engine’s strong suit and tend to fail. A valve cover gasket is found in between the engine and valve cover and seals the oil inside. They fail typically due to lack of maintenance which will make the gasket worn or tear. If it does happen to tear, you will have an oil leak, which is never good for an engine. If maintained properly, this shouldn’t happen in an engine, however, it is pretty common in 2.7T.
Symptoms of Valve Cover Gasket Failure:
- CEL/MIL illuminating
- Oil burning smell coming from the engine bay
- Valve cover is dirty (leaking oil)
- Low oil pressure light illuminating
- Engine misfires
When a valve cover gasket starts to leak, the only thing to do is replace it with a brand new one. Now when it comes to replacing the gasket, we recommend not only replacing the left and right seal, but also the camshaft end cap seal, camshaft seals, and camshaft chain tensioner gasket since everything will be in one place. This is a rather difficult DIY if you don’t know where all the components listed above are. A mechanic will likely charge $250 just to replace the valve cover gasket.
Buy Here: B5 S4 Valve Cover Gasket Kit Replacement
DIY Difficulty: Difficult
7. Faulty Coolant Temperature Sensor
Faulty coolant temperature sensors is not specifically a VW or Audi problem, it is common across many OEMs. A coolant temperature, or CTS, gauges the temperature of coolant/antifreeze going through the engine. It is the sensor that provides the engine temperature reading on the dash of a vehicle. Since an engine runs extremely hot and these sensors are made out of hard plastic, the main reason they fail is due to wear and tear. If a CTS does happen to go out, false signals can be sent to the ECU, which would result in incorrect fuel and timing settings. A vehicle will likely go through at least one sensor in its lifecycle.
Symptoms of Coolant Temperature Sensor Failure:
- CEL/MIL illuminating with P1296, P2181, P2185, or P0139 fault codes
- Engine overheating
- Sporadic engine temperature readings on the dash
- Rough engine performance
When a CTS goes out, there is only one solution and that is to replace it. It’s not too hard to replace if you know where it is located. A replacement CTS is cheap and shouldn’t take any longer than 30 minutes to install.
Buy Here: B5 S4 Coolant Temperature Sensor Replacement
DIY Difficulty: Easy
Audi B5 S4 Reliability
The Audi B5 S4 engine is very reliable if maintenance schedules are followed religiously. We will say that if your stock turbos have not gone, they most likely will at some point in the vehicle’s lifecycle, as we’ve explained above. However, with upgraded turbos or a second set of K03 turbos, we’ve seen these last 200,000+ miles. Common maintenance items to stay on top of are: ignition coils & spark plugs, oil changes every 5,000 miles, timing belts & tensioners, water pump, fuel pump. Every engine is made differently, so this is not to say that every 2.7T engine will last till 200,000 miles.
If you are interested in reading up on more Audi content, here is our write-up on The 5 Best Performance Mods for the Audi B8/B8.5 S4.