Audi2001–2021 Critical issues documented

Audi S4 B8: common faults & what to check

The B8 is the Audi S4 built 2008–2016. Of the 10 faults documented for the S4, 7 apply to this generation, each with its symptoms, what to inspect and a typical repair cost. Free, no account needed.

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Documented faults

Critical

Most serious

$550–$1,900

Typical repair

Service milestones

You're looking at the B8

Everything below is narrowed to this variant. Pick a different one to change it.

2008–2016B8 Selected2008–2016B8Engine not documented for this generationEngine not documentedDocumented issues7 knownSee faults & what to checkPhoto: Shawn Jooste via Wikimedia Commons, CC BY 2.0.

Choose a different generation

Now narrow it to the engine

A 1.8 and a 2.4 of the same car do not fail the same way, so the faults below narrow to the engine as well as the year. Free, no account needed.

Which engine is in it? These cover every year of this model.

3.0L V6 supercharged· 3.0 litre, turbocharged 3.0L V6 turbo· 3.0 litre, turbocharged 4.2L V8· 4.2 litre

A 2009 Audi S4 is the B8 generation (2008 to 2016).

We cannot narrow the engine list to this year, so every engine this model was sold with is offered.

Start your free check on this Audi S4

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Audi S4 B8Engine not picked yet

Pick the engine above first: the S4 came with 3, and without it the report has to show all of their faults. Pick the engine

Can't confirm for this car

Audi S4 · 2009

Narrowed to the year. No engine is recorded for this vehicle. Pick an engine to see which faults apply.

Tell us the engine, or check the engine code on the car, before relying on this.

No engine is recorded for this vehicle.

matched on year only

What to look out for

The checks worth doing on a Audi S4 before you hand over any money. Every documented fault is listed below, each with its own page.

Costly issue
Inspect the front control arm bushes visually for splitting, tearing, or separation of the rubber from the steel insert.
See why
Front Lower Control Arm Ball Joint and Bush Wear
The front suspension on B6, B7, and B8 A4 models uses aluminium lower control arms (wishbones) with pressed-in rubber-bonded bushes and an integral ball joint at the outboard end. Both the front bush and the ball joint wear faster than expected on these arms, particularly on vehicles used in urban driving with frequent low-speed cornering and kerbing. On OEM control arms, the ball joint cannot be replaced separately — once the ball joint wears beyond limits, the entire control arm must be replaced. The front bush deteriorates under load cycling and can allow the arm to move fore-aft, degrading steering response and causing tyre wear. Worn ball joints, if left uncorrected, eventually develop enough play to separate under load, causing sudden loss of front-wheel steering geometry control.
What you would notice
- Clunking or knocking from the front suspension when driving over potholes, speed bumps, or rough road surfaces
- Vague or imprecise steering, particularly on initial turn-in, caused by front bush deflection under load
- Uneven tyre wear across the front axle, often showing greater wear on the inner or outer shoulder
- Steering pulling to one side under hard braking, suggesting one side is worn more than the other
Typically $550–$1,900 to put right.
Costly issue
During a test drive, note whether the rear of the car tramlines, wanders, or feels unsettled over undulations and during braking from speed.
See why
Rear Subframe Bush Deterioration
The B6, B7, and B8 A4 rear subframe is located and compliant-mounted to the body via large rubber bushes at four mounting points. These bushes carry significant longitudinal and lateral loads from the rear suspension and are subject to long-term rubber degradation from ozone, heat, and fatigue. As the bushes deteriorate, the subframe develops controlled but unintended movement under braking and acceleration loads. This directly affects rear wheel alignment — particularly toe angle — causing the rear wheels to steer slightly as the subframe shifts, producing instability and tyre scrub. The condition is often missed at standard service inspections but can be confirmed by physically inspecting or applying load to the subframe during a workshop check.
What you would notice
- Rear-end instability or wandering during motorway driving, requiring constant minor steering corrections
- Clunking or thudding from the rear of the car during hard braking or sharp acceleration
- Uneven rear tyre wear, typically feathering or diagonal wear on the inner edge from dynamic toe changes
- Loose or imprecise steering feel that worsens at higher speeds
Typically $700–$2,000 to put right.

A 2009 Audi S4: what is due, and when

Servicing

Nothing left on the schedule

Every milestone is behind this car. The ones below are the receipts worth asking for.

Placed by the car’s age, not read from the dash — 117,300–273,700 km after 17 years.

Timing

Our research does not record which this engine uses, and it depends on the engine rather than the model. Check the owner’s manual rather than assume: on a belt-driven engine, an overdue belt is the failure that takes the engine with it.

Behind it

80,000 kmFull service of the S-tronic transmission fluid and filter for longevity.
100,000 kmInspect the engine mounts and check for carbon buildup on the intake valves, common for direct-injection engines.
120,000 kmSuspension control arms and bushings show age here, which can affect the sharp handling these cars are known for.

“Behind it” means the car has driven past that distance, not that the work was done — ask to see the receipts. These are the intervals for the B8 · 3.0L TFSI V6 Supercharged - Quattro · Petrol; only the car’s own service book says what has actually been done to it.

See all 7 issues for this oneDocumented for the exact year and engine you picked, including 1 rated critical.

Electrical1

01MMI 2G/3G Display and Control Unit Failure

The B8 A4 introduced Audi's MMI (Multi Media Interface) infotainment system in both 2G and 3G hardware generations.2008–2016Electrical$400–$2,800

CommonElectrical $400–$2,800 to fix

The B8 A4 introduced Audi's MMI (Multi Media Interface) infotainment system in both 2G and 3G hardware generations. The display module uses a TFT screen with ribbon cable connections that are prone to fatigue cracking from repeated thermal cycling and vibration. Failure typically presents as vertical pixel lines, partial blackouts, or a completely black screen while the audio and navigation systems continue to function (confirming the processor is running but the display has failed). In other cases the control unit itself fails — the MMI becomes unresponsive to inputs, reboots continuously, or loses stored settings after ignition cycles. The 3G MMI navigation hard drive can also fail, causing the satellite navigation to become unavailable while the rest of the unit continues to operate.

Symptoms to notice

Vertical or horizontal lines of dead pixels across the display, or a partially or fully black screen while audio continues to play
MMI system freezing mid-operation, becoming unresponsive to rotary controller or button inputs
Spontaneous MMI reboots — the Audi rings boot screen appears repeatedly during a journey
Navigation system unavailable or showing an error message while radio and phone functions continue to operate

What to check

Switch on the ignition and inspect the MMI display for missing pixel columns, discolouration, or partial blackout — these are characteristic of ribbon cable failure.
Cycle through all MMI menus to check for freezing or sluggish response.
Test the navigation system — a failed hard drive will show an error or fail to load maps.
Check that the MMI retains settings (radio stations, navigation home address) after the car is locked and reopened.
Inspect the screen edges for separation or any signs that the unit has been previously opened.

Where to look: Centre stack dashboard (display screen) and boot-mounted MMI control unit/hard drive

Ask the seller

“Does the MMI display show any lines, dark patches, or go black at any point?”
“Does the MMI ever freeze or reboot itself during a drive?”
“Is the satellite navigation fully functional, including map loading?”

Body, brakes, suspension & interior2

02Rear Subframe Bush Deterioration

During a test drive, note whether the rear of the car tramlines, wanders, or feels unsettled over undulations and during braking from speed.2001–2016Suspension$700–$2,000

CommonSuspension $700–$2,000 to fix

The B6, B7, and B8 A4 rear subframe is located and compliant-mounted to the body via large rubber bushes at four mounting points. These bushes carry significant longitudinal and lateral loads from the rear suspension and are subject to long-term rubber degradation from ozone, heat, and fatigue. As the bushes deteriorate, the subframe develops controlled but unintended movement under braking and acceleration loads. This directly affects rear wheel alignment — particularly toe angle — causing the rear wheels to steer slightly as the subframe shifts, producing instability and tyre scrub. The condition is often missed at standard service inspections but can be confirmed by physically inspecting or applying load to the subframe during a workshop check.

Symptoms to notice

Rear-end instability or wandering during motorway driving, requiring constant minor steering corrections
Clunking or thudding from the rear of the car during hard braking or sharp acceleration
Uneven rear tyre wear, typically feathering or diagonal wear on the inner edge from dynamic toe changes
Loose or imprecise steering feel that worsens at higher speeds

What to check

During a test drive, note whether the rear of the car tramlines, wanders, or feels unsettled over undulations and during braking from speed. Inspect rear tyre wear patterns — diagonal or feathered wear on the inner or outer edge suggests subframe movement affecting toe alignment. If a workshop inspection is possible: Have a technician inspect the rear subframe mounting bushes on a hoist — deteriorated bushes will show cracking, splitting, or visible separation of the rubber from the steel carrier. Apply a pry bar to the subframe to check for movement at the mount points.

Where to look: Rear subframe-to-body mounting points, four bushes at front and rear of the subframe

Ask the seller

“Have the rear subframe bushes ever been inspected or replaced?”
“Has the car had rear wheel alignment checked recently — and did the workshop note any bush wear?”
“Does the car feel stable at motorway speeds, or does it wander or feel loose at the rear?”

03Front Lower Control Arm Ball Joint and Bush Wear

Inspect the front control arm bushes visually for splitting, tearing, or separation of the rubber from the steel insert.2001–2016Suspension$550–$1,900

Very commonSuspension $550–$1,900 to fix

The front suspension on B6, B7, and B8 A4 models uses aluminium lower control arms (wishbones) with pressed-in rubber-bonded bushes and an integral ball joint at the outboard end. Both the front bush and the ball joint wear faster than expected on these arms, particularly on vehicles used in urban driving with frequent low-speed cornering and kerbing. On OEM control arms, the ball joint cannot be replaced separately — once the ball joint wears beyond limits, the entire control arm must be replaced. The front bush deteriorates under load cycling and can allow the arm to move fore-aft, degrading steering response and causing tyre wear. Worn ball joints, if left uncorrected, eventually develop enough play to separate under load, causing sudden loss of front-wheel steering geometry control.

Symptoms to notice

Clunking or knocking from the front suspension when driving over potholes, speed bumps, or rough road surfaces
Vague or imprecise steering, particularly on initial turn-in, caused by front bush deflection under load
Uneven tyre wear across the front axle, often showing greater wear on the inner or outer shoulder
Steering pulling to one side under hard braking, suggesting one side is worn more than the other

What to check

Inspect the front control arm bushes visually for splitting, tearing, or separation of the rubber from the steel insert. During the test drive, note any clunking from the front suspension over speed bumps or rough surfaces, or vagueness in the steering on turn-in. Check front tyre wear — uneven wear across the tread width can indicate compromised control arm geometry. If a workshop inspection is possible: Have the car raised on a hoist and grip the front tyre at 12 and 6 o'clock to check for play in the ball joint — any detectable movement indicates replacement is needed.

Where to look: Front lower control arms, one per side — ball joint at the wheel hub end, bushes at the subframe end

Parts involved: Ball joint.

Ask the seller

“Have the front control arms or ball joints been replaced? At what mileage?”
“Has the car ever clunked from the front over bumps or speed humps?”
“When was the last wheel alignment performed, and were any suspension faults noted?”

Depends on the exact engine — 4 moreDocumented for a specific engine we could not confirm from what you picked. Check the engine code on the car.

Engine, transmission & cooling4

013.0 TFSI Thermostat Housing and Water Pump Coolant Leak

The 3.0 TFSI runs a combined plastic thermostat housing and water pump module at the front of the engine.petrol2009–2016CoolingCan't confirm for this car$1,100–$2,400Read the full fault: symptoms, where to look, what to ask the seller

023.0 TFSI Supercharger Coupler Wear and Rattle

petrol2009–2016EngineCan't confirm for this car$900–$2,200Read the full fault: symptoms, where to look, what to ask the seller

03PCV / Oil Separator Valve Failure

Inspect the valve cover oil separator housing for cracks and check the large vacuum hose from valve cover to intake for oil contamination.petrol2008–2015EngineCan't confirm for this car$400–$1,200

Very commonEngine $400–$1,200 to fix

Can't confirm for this car

The EA888 positive crankcase ventilation (PCV) system incorporates an oil separator integrated into the valve cover. The membrane diaphragm and check valves crack with age and heat cycling. A failed PCV draws oil vapour directly into the intake manifold, fouling the throttle body and intake valves with carbon deposits on direct-injection engines, and causes excessive oil consumption through the intake tract. Intake valve carbon build-up reduces airflow and causes misfires. Gen 3 engines (CYMC, B9) retained this vulnerability.

Symptoms to notice

Blue-grey smoke from exhaust under deceleration
Oil level dropping between services with no visible external leak
Hissing or sucking noise from valve cover area
Rough idle and misfires after extended use

What to check

Inspect the valve cover oil separator housing for cracks and check the large vacuum hose from valve cover to intake for oil contamination.
Check oil level and ask when it was last topped up relative to service interval.
If a workshop inspection is possible: Remove the intake hose at the throttle body and inspect the throttle plate for oily carbon deposits.

Where to look: Integrated into top of valve cover, PCV hose runs to intake manifold

Parts involved: PCV / oil separator.

Ask the seller

“Has the PCV valve or oil separator been replaced?”
“How much oil is consumed between services?”
“Has the intake manifold or throttle body been cleaned?”

04S tronic DL501 mechatronic unit failure (B8 S4 7-speed S tronic)

Test drive in slow stop-start traffic and note any shuddering when pulling away from rest.2009–2016TransmissionCan't confirm for this car$3,000–$8,000

CommonTransmission $3,000–$8,000 to fix

Can't confirm for this car

The 7-speed S-tronic dual-clutch transmission (DL501 / 0B5 code) used longitudinally in the A4 pairs a wet multi-plate clutch pack with an electro-hydraulic mechatronic control unit. The mechatronic valve body develops internal hydraulic leaks and solenoid faults causing shuddering at low speed, harsh or refused gear engagement, and in severe cases complete loss of drive. Clutch pack wear also produces juddering when pulling away from rest. Audi extended the warranty in some markets but units outside warranty require full replacement. B9 variants retained DL501 and share the same failure mode.

Symptoms to notice

Shuddering or vibration when pulling away at low speed
Harsh, jerky downshifts especially in traffic
Transmission warning light or failsafe mode
Delayed or refused engagement from Park or Neutral

What to check

Test drive in slow stop-start traffic and note any shuddering when pulling away from rest.
Perform multiple low-speed creep manoeuvres.
Check for stored transmission fault codes (P17BF, P175B, P1717 are common mechatronic codes on DL501).
Confirm the mechatronic oil (Haldex/DSG fluid) has been serviced at recommended intervals.
Ask if Audi extended warranty work was carried out.

Where to look: Transmission housing, mechatronic unit on left side of gearbox

Parts involved: Mechatronic / valve body.

Ask the seller

“Has the S-tronic mechatronic unit ever been replaced or remanufactured?”
“Has S-tronic fluid been changed at the Audi-recommended interval?”
“Has the transmission ever been in failsafe or warning mode?”

Other Audi S4 engines and years3 documented issues that do not apply to the one you picked.

Engine, transmission & cooling1

01Electric auxiliary coolant pump failure — overheating

After a test drive of at least 15 minutes, check the coolant temperature gauge behaviour throughout the drive and after shutdown.petrol2015–2016CoolingDoes not apply$600–$1,800

OccasionalCooling $600–$1,800 to fix

Does not apply

The B9 A4 2.0 TFSI uses an electric auxiliary coolant pump (EWP) to circulate coolant through the turbocharger and heater core when the main belt-driven pump cannot maintain adequate flow, and to provide post-run cooling after engine shutdown. These electric pumps are known to fail due to impeller wear or motor burnout, particularly on vehicles above 80,000 km. Failure triggers a coolant temperature warning and can cause the engine to overheat if ignored. The turbocharger may also suffer heat-soak and bearing damage after engine shutdown if the post-run circulation pump has failed silently.

Symptoms to notice

Coolant temperature warning light or gauge reading higher than normal operating range
Reduced heater output with cold or intermittent air from cabin vents
Fault codes for auxiliary coolant pump circuit open or short (P260D or manufacturer-specific code)
Overheating warning during or shortly after sustained high-speed or hard driving
Absence of the normal electric pump whirring sound from the engine bay during post-shutdown cooling cycle

What to check

After a test drive of at least 15 minutes, check the coolant temperature gauge behaviour throughout the drive and after shutdown. Scan for fault codes relating to the auxiliary water pump circuit. On a warmed engine shortly after shutdown, listen near the firewall area for the auxiliary pump running. Inspect the coolant expansion tank for correct level and absence of oil contamination or rusty discolouration.

Where to look: Engine bay — electric auxiliary coolant pump mounted near the firewall or within the turbocharger cooling circuit

Parts involved: Water pump.

Ask the seller

“Has a coolant temperature warning or overheating light ever appeared on this vehicle?”
“Has the auxiliary electric coolant pump been inspected or replaced during ownership?”
“Has the coolant been flushed and renewed on the manufacturer-recommended schedule?”

Electrical1

0112V AGM Battery Premature Failure and BMS Coding Fault

Test the battery with a proper conductance tester (not just a voltage check) — the result should show state of health above 75%.2015 onwardElectricalDoes not apply$380–$750

CommonElectrical $380–$750 to fix

Does not apply

The B9 A4 carries a large number of always-on control modules that impose a significant parasitic drain, causing the OEM AGM start-stop battery (located in the boot) to fail within 3–4 years in typical ownership. The Battery Management System (BMS) controller must be coded to the exact replacement battery specification via VCDS or dealer tooling — fitting a replacement without coding leaves the BMS charging on an incorrect profile, shortening the new battery's life significantly and preventing the start-stop system from re-enabling.

Symptoms to notice

Slow or laboured cold cranking with a healthy engine
Start-stop system permanently deactivated without a driver-initiated reason
MMI infotainment system resetting or freezing after a cold overnight soak
Central locking and comfort window operation intermittently failing
Battery or electrical system warning light on the instrument cluster

What to check

Test the battery with a proper conductance tester (not just a voltage check) — the result should show state of health above 75%.
Confirm the start-stop system activates: if it is permanently suppressed with no fault explanation, assume the battery is weak or uncoded.
Scan the BMS controller for battery age, charge cycle count, and replacement history.

Where to look: Boot/trunk — battery mounted under the floor panel on the right side

Parts involved: 12V battery.

Ask the seller

“Has the 12V battery ever been replaced, and if so was it coded to the car using dealer or VCDS tooling?”
“Is the start-stop system currently functioning, or is it permanently disabled?”
“Has the car ever had difficulty starting overnight or after sitting for a few days?”

Body, brakes, suspension & interior1

01B9 S4 rear axle nuts may break on some 2019-2021 cars, recall REC-001665 (check VIN)

Look at both rear tyres for uneven wear across the tread, especially the inner edges.2019–2021SuspensionDoes not apply$0–$600

RareSuspension $0–$600 to fix

Does not apply

On some 2019 to 2021 B9 Audi S4s (and other A4, A5 and larger Audis of those years) nuts fitted to the rear axle did not meet specification and can break, letting the rear wishbone move against the hub carrier and suddenly changing the rear wheel alignment. Audi Australia recalled 1,622 cars in September 2021 (REC-001665, campaign 42L1) to replace the nuts free of charge. A follow-up recall in March 2022 (REC-005076, campaign 42L5) corrects rear misalignment and tyre wear caused by some of the first repairs. 2017 and 2018 cars are not part of this recall. Only cars listed by VIN are affected.

Symptoms to notice

Clunk from the rear over bumps
Car pulls or the rear feels unsettled
Uneven or fast wear on the inner edges of the rear tyres

What to check

Look at both rear tyres for uneven wear across the tread, especially the inner edges. On the test drive, listen for clunks from the rear over bumps and check the car tracks straight. Ask for dealer paperwork showing Audi recalls 42L1 and 42L5 (REC-001665 and REC-005076) were done. If a workshop inspection is possible: have a four-wheel alignment check and ask an Audi dealer to run the VIN for open recalls.

Where to look: Rear axle, where the wishbones bolt to the rear hub carriers

Ask the seller

“Have Audi recalls 42L1 and 42L5 for the rear axle nuts been done?”
“Has the car had a rear wheel alignment recently, and were the rear tyres wearing unevenly?”
“Has an Audi dealer checked the VIN for open recalls?”

Audi S4 faults in detail

Narrowed to the Audi S4 · 2009. Each of these has its own page: the symptoms, where to look, what to ask the seller and what the repair costs. Free, no account needed.

3.0 TFSI Supercharger Coupler Wear and RattleMajor · Engine 3.0 TFSI Thermostat Housing and Water Pump Coolant LeakMajor · Cooling

What these repairs cost on other cars

Some of the Audi S4’s documented faults are repairs other models share. Each page lists the documented NZ cost for every model it affects.

DSG and Dual-Clutch Gearbox Repair Cost

Other Audi models

Audi A445 documented faults Audi A343 documented faults Audi A634 documented faults Audi RS39 documented faults Audi S69 documented faults Audi A87 documented faults

Audi S4 buyer questions

Is the Audi S4 reliable?

Like any used car, it depends on the specific example and its service history. Across the 10 documented faults for the Audi S4, the recurring problem areas are transmission, suspension, and cooling. A Audi S4 with a full service history and no signs of the issues listed on this page can be a sound buy but each one needs to be checked individually before you commit.

What are the most common problems with a used Audi S4?

We've catalogued 10 known faults for the Audi S4, covering transmission, suspension, and cooling. All 10 are written out in full on this page, with the symptoms to notice, what to inspect, and typical repair costs for each. Free to read, no account needed.

How much do repairs cost on a Audi S4?

Most single repairs on the Audi S4 fall between $550–$1,900 at NZ independent-workshop rates. Some of the 10 documented faults cost less and a few cost considerably more, and no one car needs them all. Knowing which ones to look for before you view is what lets you negotiate the price down or walk away.

Should I get a pre-purchase inspection on a Audi S4?

Yes. A Audi S4 inspection focused on its known weak points is the single best way to avoid an expensive mistake. KickTyres gives you a guided, model-specific inspection plus a market valuation and negotiation figure for $24.90 far less than the cost of missing one of the faults on this page.