Audi S4 4.2 V8 B6 Reliability

Common Problems

Timing chain tensioner and guide failure

€3,500 - 6,0001 of 6

Plastic guides and tensioners wear out, causing chain rattle and potential engine damage · more· less

The BBK 4.2 V8 has its timing chain system at the rear of the engine, facing the firewall, meaning the entire engine must be removed for service. The plastic chain guides crack and break, tensioners lose pressure, and chains stretch over time. Early symptoms include a rattle on cold start lasting a few seconds, progressing to persistent rattle and eventually camshaft correlation fault codes (P0016/P0017). B6 models (2003-2005) are more prone to failure than later B7s, which received revised components from 2006 production onward. Failures have been documented as early as 60,000 km, though many engines reach 150,000 km without issues. Parts kits cost around €800-1,200, but the 25-30 hours of labor (engine out, timing service, reinstall) drives the total to €3,500-6,000 at a specialist. Audi dealers have quoted significantly more. Preventive service is recommended by most specialists before 120,000 km regardless of symptoms.

Excessive oil consumption

€200 - 4,0002 of 6

Many engines consume 0.5-1.0 litre per 1,000 km, with some far worse · more· less

Oil consumption is widely reported on B6 S4 engines, with Audi at one point stating that 1 litre per 1,000 km was within specification. Common causes include worn valve stem seals (the most frequent culprit), weak PCV system allowing crankcase pressure to push oil into the intake, and worn piston rings on higher-mileage engines. Topping up oil regularly (€200-400/year in oil costs) is manageable, but if consumption exceeds 1 litre per 1,000 km, the underlying cause should be diagnosed. Valve stem seal replacement costs around €1,500-2,500 (labor-intensive but does not require engine removal). A full engine rebuild for piston rings or scored cylinders can reach €4,000 or more. Regular oil changes with quality synthetic oil at 7,500-10,000 km intervals help manage consumption.

Front control arm bushing wear

€800 - 1,8003 of 6

Multi-link front suspension has 8 control arms with bushings that wear by 80,000-120,000 km · more· less

The B6 platform uses a multi-link front suspension with 4 control arms per side (8 total). The bushings, particularly the upper arms, are known to wear prematurely, causing clunking over bumps, imprecise steering, and uneven tire wear. A TSB exists for the upper arm bushings, which can crack or allow the metal spacer to unbond from the rubber. Audi designs these arms so the bushings cannot be replaced separately. A full set of 8 aftermarket control arms with hardware costs around €400-600, with labor of €400-600 for the complete front end. OEM arms are significantly more expensive. Alignment is required after replacement. On a car of this age, expect to replace the full set at least once during ownership if it has not already been done.

Valve cover gasket leaks

€400 - 9004 of 6

Gaskets harden with age and heat, causing oil leaks around both V8 valve covers · more· less

The valve cover gaskets on the 4.2 V8 harden and shrink over time, leading to oil seepage and eventually dripping onto the exhaust manifolds, which can cause burning oil smell and smoke. Both sides (16 cam end plug seals and 8 spark plug tube seals total) typically need attention at the same time. The valve covers themselves can warp on higher-mileage engines, requiring resurfacing or replacement. Parts for a complete gasket kit cost around €100-150. Labor runs €300-750 depending on the shop, as intake manifold removal is needed for access on one bank. This is considered routine maintenance on a V8 of this age.

Auxiliary radiator leaks

€300 - 7005 of 6

Side-mounted auxiliary radiators develop leaks at plastic fittings and hose connections · more· less

The B6 S4 has two auxiliary radiators mounted in the front fender area that supplement the main radiator for the V8's cooling needs. These are prone to developing leaks at the plastic end fittings and hose connections, particularly as they age. Symptoms include coolant loss visible at the lower front edges of the wheel wells. The radiators themselves are relatively inexpensive (€80-120 each), but some aftermarket replacements have poor quality end caps that fail within months. OEM or quality aftermarket units are recommended. If a thermostat has previously seized, the resulting overpressure can accelerate auxiliary radiator failure. Labor is moderate as the components are reasonably accessible.

Ignition coil pack failure

€200 - 5006 of 6

Coil packs fail individually, causing misfires on affected cylinders · more· less

The BBK V8 uses 8 individual coil-on-plug ignition coils. These are a known wear item across many VAG engines and can fail at any mileage. Symptoms include rough idle, misfires on specific cylinders, and a flashing check engine light. Individual coils cost €20-40 each, and most specialists recommend replacing all 8 along with spark plugs when one fails, bringing the total to €200-500 including labor. Spark plugs should be changed every 40,000-60,000 km as part of regular maintenance. This is a relatively minor issue that is easy and inexpensive to diagnose and fix.

High-maintenance V8 that rewards proactive owners

The B6 S4's 4.2 V8 is a characterful engine, but ownership demands a proactive approach to maintenance. The timing chain service dominates the cost picture and should be considered a when-not-if expense on any car that has not already had it done. Oil consumption, control arm wear, and coolant system maintenance add to the running costs. Cars with documented timing chain service and consistent maintenance history are significantly lower-risk purchases than those with unknown histories.

Pre-Purchase Inspection Checklist

General checks

Service history
Complete records from Audi dealer or specialist essential. Verify oil change intervals (every 10,000 km maximum with full synthetic).
Cold start the engine
Must be started completely cold. Listen carefully for any rattling in the first 30 seconds. This is the most important single check.
Test drive
Minimum 30 minutes including varied speeds. Listen for suspension clunks, check gearbox shifts (manual: synchro feel in all gears, auto: smooth shifts in Sport mode).
Tires and alignment
Check for uneven tire wear indicating worn control arms or alignment issues. Inspect tire age and condition.

Specific for this vehicle

Listen for timing chain rattle on cold start
A brief rattle (2-3 seconds) is borderline. Persistent rattle beyond 5 seconds indicates worn tensioners or guides and likely costly service ahead.
Check oil level and consumption history
Ask the owner about oil consumption rate. Check the dipstick for level and oil condition. Blue/grey exhaust smoke on startup suggests valve stem seal wear.
Inspect for oil leaks around valve covers
Look for oil residue on both valve covers, around spark plug tubes, and on the exhaust manifolds. Burning oil smell is a common sign.

+ 4 more checksShow less

Test front suspension over bumps
Drive over speed bumps and rough surfaces. Clunking or knocking from the front indicates worn control arm bushings.
Check coolant level and auxiliary radiators
Inspect coolant level in the expansion tank. Look under the front fender areas for coolant stains indicating auxiliary radiator leaks.
Verify timing chain service status
Ask for documentation of timing chain, tensioner, and guide replacement. If not done and the car has over 100,000 km, budget for preventive service.
Run a full diagnostic scan
Check for camshaft correlation codes (P0016/P0017), misfire codes, and secondary air system faults. Multiple stored codes may indicate deferred maintenance.

Recalls and Technical Service Bulletins

Headlight switch wiring harness short circuit risk (2004 models, knee bolster area) Verify completed

Takata passenger airbag inflator replacement (2005 models, inflator degradation risk) Critical - verify completed

Contact Audi with the VIN to verify all recalls and service campaigns have been completed. The Takata airbag recall is particularly important as the inflator can rupture on deployment.

Warranty Status

Factory warranty (2 years) Expired on all B6 S4 models

Rust perforation warranty (12 years) Expired on all B6 S4 models

All B6 S4 models are well outside both their original 2-year factory warranty and 12-year rust perforation warranty. No manufacturer extended warranty programs are available for these vehicles. Third-party warranties are available but typically exclude timing chain and pre-existing oil consumption issues.

Sources: Research draws on model-specific owner forums and owner communities, recall information from official authorities, German automotive press, and multiple workshop cost references cross-checked against each other.

This report is for informational purposes only and does not constitute professional advice. Estimates may be inaccurate. Always have a qualified specialist inspect the vehicle before purchase. We accept no liability for decisions made based on this information.

Audi S4 4.2 V8 B6

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