Audi A4 Common Problems by Generation: B7, B8 and B9

Audi A4 faults follow the platform, not the badge. A 2006 A4 and a 2018 A4 share a nameplate and very little else — different engine family, different crankcase ventilation design, different plastics, different order of failure. The useful question is never "what goes wrong with an A4," it is "what goes wrong with this A4." This guide sorts the problems by generation and links to the repairs we have written up from our own bays.

Which generation is my Audi A4?

Audi tracks the A4 by internal chassis code, and owners get answers faster once they know theirs. Three generations cover nearly every A4 still driven daily around the Valley:

• B7 — 2005 to 2008. The oldest A4 that still shows up regularly. Everything on it is now old enough that age, not mileage, drives most of what fails.
• B8 — 2009 to 2016. The long-running generation, facelifted partway through. Turbocharged direct injection is the defining change, and it brings its own maintenance habits.
• B9 — 2017 onward. Still a modern car. Problems here are mostly wear items and ventilation, not the tired-rubber failures of the older platforms.

If you are not sure which one you have, the model year narrows it immediately, and the chassis code on the vehicle data sticker settles it.

What tends to fail on a B7 A4 (2005 to 2008)?

On a car this age, the failures cluster around materials rather than design. Plastic and rubber in the crankcase ventilation system go brittle from years of heat cycling and oil vapour, crack, and stop sealing. Gaskets harden. Once the ventilation system can no longer regulate crankcase pressure, that pressure has to go somewhere, and it goes past whatever seal is weakest.

That is exactly the sequence we traced on a B7 that came in for oil leak repair on a 2006 A4 Quattro — oil spots on the driveway and a burning smell in the cabin, with a degraded PCV assembly at the root of it. The lesson that transfers to any B7: an oil leak on this generation is usually a symptom, and replacing a gasket without asking what pressurised it is how the same leak comes back.

What tends to fail on a B8 A4 (2009 to 2016)?

The B8 is where the A4 moved to turbocharged direct injection, and the maintenance profile changed with it. Because fuel is sprayed straight into the cylinder rather than across the back of the intake valves, nothing washes those valves clean, so carbon deposits build up over the years and gradually blunt throttle response and idle quality. Owners of this generation also report timing-chain-side noise and higher-than-expected oil consumption often enough that both are worth checking rather than waiting on.

None of that makes the B8 a bad car — it makes it a car that rewards being kept on interval. Oil service on schedule, an honest look at the crankcase ventilation system, and someone listening to the chain side of the engine at each visit is most of what keeps a B8 out of the expensive category. That is ordinary scheduled maintenance work, done by someone who knows what to listen for on this platform.

What tends to fail on a B9 A4 (2017 onward)?

A B9 is young enough that most of what we see is either a wear item arriving on schedule or a ventilation fault arriving early. Both are cheap to handle and both get expensive if they are read as "the car is new, it is probably nothing."

On the ventilation side, a 2018 A4 came to us with a check engine light, a rough idle, and a whistle at idle; the fix was PCV valve replacement after a smoke test confirmed where the unmetered air was getting in. On the wear side, a 2022 A4 arrived with a squeak from one rear wheel that turned out to be glazed pads and rotor — the full story is in our write-up on A4 brake squeak repair. A four-year-old car with glazed brakes is not unusual; how it is driven matters more than how new it is.

The failure chain most A4 owners miss

Across all three generations, one relationship explains more A4 repairs than any other: a failing PCV valve can pressurise the crankcase and cause oil leaks. The valve is the cheap part. The seals and gaskets it blows past are not, and the labour to reach them is not either.

We have documented both ends of that chain on the same platform, twenty years apart — the B9 with a ruptured PCV diaphragm caught before it pushed oil anywhere, and the B7 where it had already been leaking for a while. Same mechanism, two very different repair bills. If your A4 is using oil, leaking oil, idling roughly, or throwing a lean code, the ventilation system is where a good diagnosis starts.

Which A4 symptoms should you not keep driving on?

• Oil spots under the car, or a burning smell in the cabin. Oil on hot exhaust is a fire risk, and a leak that drops the level far enough stops being a leak and starts being engine damage.
• Grinding, rather than squeaking, from a wheel. A squeak buys you time to book. Grinding means the pad backing is on the rotor and you are now paying for rotors too.
• A check engine light with a rough idle or a whistle at idle. The combination points at unmetered air, and lean running wears the engine while you wait.
• Needing to top up oil between services. Whether it is going out through a seal or up through the crankcase, both answers are worth knowing before the next interval.
• A brake pedal that feels soft, or pulls the car to one side. Neither is a noise complaint. Both are stopping-distance complaints.

Where to start if your A4 is doing something new

Match the symptom to the generation and you have a shortlist before the car is even on a lift, which is the whole point of thinking about an A4 by chassis code. Beyond the A4, the same approach carries across the range — our notes on rear bumper and wing alignment on a 2021 R8 come out of the same habit of checking why a component moved rather than just putting it back.

If your A4 is showing any of the above, or you want a straight answer on what a car of its age genuinely needs next, book it in with our team and we will start with the diagnosis rather than the parts list.