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Audi · Known Issues

2008 Audi S4 Problems: 4 Known Issues

2008 model year · NHTSA recalls, manufacturer TSBs, and owner forum reports · Updated September 2026

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Issue summary

According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 2008 Audi S4 has 4 documented known issues, with 2 rated critical. The most serious are Passenger Airbag Inflator Can Rupture (Recall 18V427 / 69R7) and 4.2 V8 Timing Chain Guides, Tensioners and Cam Adjusters Fail at the Rear of the Engine (Engine-Out Repair) ($4,500-$10,000 repair). Across all issues with published estimates, repair costs range from $500 to $10,000. DIY maintenance guides at au7o.io.

In This Article

  • S4 Safety/Recalls1
  • S4 Engine1
  • S4 Transmission1
  • S4 Emissions1
  • Recalls2
  • FAQ
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In This Article

  • Safety/Recalls1
  • Engine1
  • Transmission1
  • Emissions1
  • Recalls2
  • FAQ

All 4 Known Issues

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On the 2005-2009 Audi S4, certain 2005-2009 S4 body styles contain passenger frontal-airbag inflators that can rupture after long-term humidity and temperature exposure, propelling metal fragments into the cabin.

Common Symptoms

  • Open safety recall
  • No reliable warning before airbag deployment

How to Fix

Check VIN eligibility because body style and original registration history affect scope. Audi dealers replace the passenger frontal-airbag remedy part free of charge under campaign 69R7.

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NHTSA Verified
High ConfidenceVerifiedReviewed Jul 2026

On the 2004-2008 Audi S4, the B6/B7 S4's 4.2L V8 (BBK/BHF) drives its timing chains from the BACK of the engine, against the firewall. What owners call "timing chain failure" is really the plastic chain guides, the chain tensioners and the two camshaft adjusters wearing out and disintegrating. Forum documentation shows plastic guide fragments sitting on the chains, with cases reported at roughly 100k-112k miles. Because the chain drive is at the rear, there is no way in from the front of the car: the engine (or at minimum the whole drivetrain assembly on a subframe drop) must come out. This is the single defining failure of this generation and is NOT shared with the B5 2.7T (belt-driven) or the B8/B9 V6s. Left alone, a snapped guide lets the chain jump timing and destroys valves and pistons on an interference engine.

This issue also affects: Audi A4, Audi A1, Audi A5

Common Symptoms

  • Rattle or slapping noise from the rear of the engine, worst on cold start
  • Camshaft position / timing correlation fault codes
  • Check engine light with timing-related codes
  • Plastic fragments found on the chains or in the oil pan during inspection
  • Rough running or no-start if the chain has jumped

How to Fix

There is no recall or warranty extension - this is an out-of-warranty owner expense. The correct repair is engine-out: replace all chain guides (metal replacement guides such as the JHM intermediate kit are preferred over the failure-prone plastic OEM part), both chain tensioners, and BOTH camshaft adjusters while access is available. Because the labor is the entire cost, most shops and owners do the clutch and rear main seal at the same time. Do not attempt a partial repair that leaves the original adjusters in - they are the second most common failure and require the same engine pull.

Typical repair cost:$4,500 - $10,000

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Community Reported
High ConfidenceVerifiedReviewed Aug 2026

On the 2004-2008 Audi S4, manual-transmission B6 and B7 S4s use a dual-mass flywheel behind the 4.2 V8, and the internal damper springs fail. The failure is progressive and intermittent early on - owners describe shudder and vibration that appear for days, vanish, then come back and stay - before settling into a constant rattle at idle that quiets when the clutch pedal is depressed. On the B6 in particular, flywheels have been documented separating outright, which can do serious damage to the bellhousing area. The DMF is a wear item that must be replaced with the clutch, not resurfaced or reused, and catastrophic failures generally follow from running one past its service life.

Common Symptoms

  • Rattle from the bellhousing at idle that stops when the clutch is pressed
  • Shudder or vibration on takeoff, often intermittent at first
  • Vibration through the shifter or floor
  • Clutch judder that progressively worsens

How to Fix

No recall. Replace the dual-mass flywheel together with the clutch kit, release bearing and, while the transmission is out, the rear main seal. Because access requires dropping the transmission (an engine-out or subframe-drop job on this platform), most owners combine it with the timing chain guide service if that is also due. A common owner alternative is a single-mass flywheel conversion with a matched clutch, which removes the failure mode entirely at the cost of added drivetrain noise.

Typical repair cost:$1,800 - $4,000

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Community Reported
Medium ConfidenceVerifiedReviewed Aug 2026

On the 2004-2008 Audi S4, the secondary air injection (SAI) system pumps air into the exhaust ports on cold start to light off the catalysts, and it is a chronic check-engine-light source on these cars. Each bank has its own combi valve. Carbon causes the combi valve to stick open, which lets hot, moist exhaust gas flow backward and condense inside the pump housing, rusting the motor bearings - the source of the loud jet-engine or whining noise on cold start. A separate and commonly misdiagnosed variant produces the same P0491/P0492 insufficient-flow codes with NO pump noise at all: the air passages inside the cylinder heads are carboned shut, and replacing the pump will not fix it. Brittle hard vacuum lines to the combi valves are a third cause.

This issue also affects: Audi A8, Audi Q7, Volkswagen Jetta

Common Symptoms

  • Loud whining, jet-engine or grinding noise from the engine bay for the first ~30-90 seconds after a cold start
  • Check engine light with secondary air flow codes
  • Failed emissions / readiness monitor not setting
  • Noise absent but codes still return after clearing

How to Fix

Diagnose before buying parts. Loud pump noise plus codes points to a water-damaged pump - and if the pump is replaced, the combi valve on that bank MUST be replaced too or the new pump will rust out the same way. Codes with a quiet, functioning pump point to clogged head passages, which require removing the combi valves and mechanically clearing the ports. Also inspect and replace the hard vacuum lines and the changeover solenoid, which are cheap and commonly cracked. Failing SAI will fail an emissions test even though driveability is normal.

Typical repair cost:$500 - $2,000

Research This Issue

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Community Reported
Medium ConfidenceVerifiedReviewed Aug 2026
NHTSA Recalls2 recalls

AIR BAGS:FRONTAL:PASSENGER SIDE:INFLATOR MODULE

Volkswagen Group of America, Inc. (Volkswagen) is recalling certain 2005-2008 Audi A4 Sedan, A4 Avant, S4 Avant and S4 Sedan, 2007-2008 RS4 Sedan, 2004 RS4 Cabriolet, 2007-2009 A4 Cabriolet and S4 Cabriolet, 2005-2011 A6 Sedan, 2006-2011 A6 Avant, and 2007-2011 S6 Sedan vehicles. These vehicles are equipped with certain air bag inflators assembled as part of the passenger frontal air bag modules used as original equipment or replacement equipment. In the event of a crash necessitating deployment of the passenger frontal air bag, these inflators may explode due to propellant degradation occurring after long-term exposure to absolute humidity and temperature cycling.

Campaign #18V42700022/06/2018

AIR BAGS:FRONTAL:PASSENGER SIDE:INFLATOR MODULE

Volkswagen Group of America, Inc. (Volkswagen) is recalling certain 2009 Audi A4 Cabriolet, S4 Cabriolet, A6 Avant, A6 Sedan and S6 Sedan vehicles originally sold, or ever registered, in Arizona, Arkansas, Delaware, the District of Columbia, Illinois, Indiana, Kansas, Kentucky, Maryland, Missouri, Nebraska, Nevada, New Jersey, New Mexico, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Virginia, and West Virginia, or "Zone B." Additionally, unless included in "Zone B" above, Volkswagen is recalling certain 2005-2008 Audi A4 Avant, A4 Sedan, A6 Sedan, S4 Avant and S4 Sedan vehicles, 2007-2008 A4 Cabriolet, RS4 Sedan, S4 Cabriolet and S6 Sedan vehicles, and 2006-2008 A6 Avant and 2008 RS4 Cabriolet vehicles originally sold, or ever registered, in Alaska, Colorado, Connecticut, Idaho, Iowa, Maine, Massachusetts, Michigan, Minnesota, Montana, New Hampshire, New York, North Dakota, Oregon, Rhode Island, South Dakota, Utah, Vermont, Washington, Wisconsin, and Wyoming. These vehicles are equipped with certain air bag inflators assembled as part of the passenger frontal air bag modules used as original equipment or replacement equipment. In the event of a crash necessitating deployment of the front air bags, these inflators may rupture due to propellant degradation occurring after long-term exposure to absolute humidity and temperature cycling.

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Frequently Asked Questions

What are the most common Audi S4 problems?

According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 2008 Audi S4 has 4 documented issues. The most frequently reported are: Passenger Airbag Inflator Can Rupture (Recall 18V427 / 69R7), 4.2 V8 Timing Chain Guides, Tensioners and Cam Adjusters Fail at the Rear of the Engine (Engine-Out Repair), Dual-Mass Flywheel Springs Break on the 6-Speed Manual 4.2 V8. Of these, 2 are rated critical and should be addressed promptly.

Is the Audi S4 reliable?

The 2008 Audi S4 has 4 known issues compiled from NHTSA recalls, manufacturer TSBs, and owner forum reports. 2 issues are rated critical: Passenger Airbag Inflator Can Rupture (Recall 18V427 / 69R7) and 4.2 V8 Timing Chain Guides, Tensioners and Cam Adjusters Fail at the Rear of the Engine (Engine-Out Repair). Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.

How much does it cost to fix common Audi S4 problems?

Repair costs for known Audi S4 issues range from $500 to $10,000, depending on the specific problem and whether you choose DIY or professional repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.

What is the 2005-2009 Audi S4 Passenger Airbag Inflator Can Rupture (Recall 18V427 / 69R7)?

Certain 2005-2009 S4 body styles contain passenger frontal-airbag inflators that can rupture after long-term humidity and temperature exposure, propelling metal fragments into the cabin. Severity: high.

What is the 2004-2008 Audi S4 4.2 V8 Timing Chain Guides, Tensioners and Cam Adjusters Fail at the Rear of the Engine (Engine-Out Repair)?

The B6/B7 S4's 4.2L V8 (BBK/BHF) drives its timing chains from the BACK of the engine, against the firewall. What owners call "timing chain failure" is really the plastic chain guides, the chain tensioners and the two camshaft adjusters wearing out and disintegrating. Forum docum… Repairs typically run $4,500-$10,000. Severity: high.

Content on this page was compiled with AI assistance using NHTSA complaints, TSBs, owner reports, and public automotive data. While we strive for accuracy, this information may contain errors. Always verify repair procedures and specifications with your vehicle's service manual or a qualified mechanic.

Data compiled from NHTSA recalls, manufacturer TSBs, automotive forums, and AI-assisted research. No aggregated owner-report counts available for this vehicle yet.

Campaign #17V03200011/01/2017

Enter your VIN at NHTSA.gov to check recalls specific to your vehicle.

What is the 2004-2008 Audi S4 Dual-Mass Flywheel Springs Break on the 6-Speed Manual 4.2 V8?

Manual-transmission B6 and B7 S4s use a dual-mass flywheel behind the 4.2 V8, and the internal damper springs fail. The failure is progressive and intermittent early on - owners describe shudder and vibration that appear for days, vanish, then come back and stay - before settling… Repairs typically run $1,800-$4,000. Severity: medium.

What is the 2004-2008 Audi S4 Secondary Air Injection System Faults - Failed Pump, Stuck Combi Valves and Carbon-Clogged Head Passages?

The secondary air injection (SAI) system pumps air into the exhaust ports on cold start to light off the catalysts, and it is a chronic check-engine-light source on these cars. Each bank has its own combi valve. Carbon causes the combi valve to stick open, which lets hot, moist e… Repairs typically run $500-$2,000. Severity: medium.