Audi S4 B9 (3.0T/2.9T) Reliability: The Rocker Arm & Water Pump Reality
Common Failure Points & Costs
| Component | Failure Mileage | Symptom | Est. Cost (USD) | Risk Level |
|---|---|---|---|---|
| Rocker Arms (Pre-2019) | 40k - 70k miles | Ticking, engine failure | $3,500 - $12,000 | Critical |
| Water Pump/Thermostat | 40k - 60k miles | Coolant leak, overheating | $1,200 - $1,800 | High |
| PCV Breather Hose | 50k - 80k miles | Oil smell, leaks | $400 - $800 | Medium |
| Control Arms | 60k - 80k miles | Clunking, wandering steering | $1,500 - $2,500 | Medium |
| Motor Mounts | 60k - 90k miles | Vibration at idle | $1,000 - $1,500 | Medium |
Reliability Verdict
The S4 B9 is a fantastic daily driver but shares the critical pre-2019 rocker arm flaw with the RS5. Post-2019 models are very reliable, barring standard German water pump issues.
Audi S4 B9 Reliability: The EA839 Architecture
The Audi S4 B9 (2018-2023) marked the move from the supercharged V6 to the turbocharged EA839 V6. While often 3.0L in this application (single turbo), it shares the same “Hot-V” architecture and, critically, the same rocker arm design as the Audi 2.9T RS5 Engine.
If you are looking for a fast, understated sedan, the S4 is a benchmark. But it is not without significant common problems.
1. The Elephant in the Room: Rocker Arm Failure
Just like its big brother the RS5, early build S4s (Pre-July 2019) are prone to rocker arm needle bearing failure.
Why it happens
The needle bearings in the rocker arm are too thin. They disintegrate, allowing the rocker to flop around and destroy the camshaft.
- Cost to Fix: $3,500 (Preventive) vs $12,000+ (After failure).
- Safe Range: 2020+ Models are factory-updated.
Read the full technical breakdown in our Rocker Arm Failure Guide.
2. Water Pump & Thermostat: The “Guaranteed” Failure
It is almost a joke among Audi enthusiasts: “If the water pump hasn’t failed, it’s not an Audi.” The B9 S4 uses a complex thermal management module.
- Failure Rate: Extremely High (nearly 100% by 80k miles).
- Symptoms: Low coolant warnings, sweet smell after driving.
- The Fix: Replacement with updated housing. Budget $1,500.
3. PCV & Oil Consumption
The PCV system is integrated into the valve cover and valley.
- Issue: The breather hoses become brittle from turbo heat and crack.
- Result: Boost leaks, oil consumption, and messy engine bays.
- Solution: Replace the entire breather assembly.
4. Maintenance Comparison (S4 vs RS5)
Is the S4 cheaper to own than an RS5? Yes.
| Service | Audi S4 B9 | Audi RS5 B9 |
|---|---|---|
| Brakes (Front) | $1,200 | $3,500 |
| Tires (Set) | $1,200 | $1,800 |
| Oil Change | $200 | $250 |
| Rocker Repair | $3,500 | $4,500 |
While the engine risks are shared, the consumables on the S4 are significantly cheaper.
5. Buying Guide: 2018 vs 2021
2018-2019 (Pre-Facelift)
- Pros: Cheaper purchase price ($25k - $35k).
- Cons: High Rocker Arm Risk. Outdated MMI.
- Verdict: Risky without proof of updates.
2020-2023 (B9.5 Facelift)
- Pros: Revised engine (Reliable). Touchscreen MMI. Better looks.
- Cons: Higher price ($40k+).
- Verdict: The one to buy.
6. Conclusion
The S4 B9 is a “9/10” car with a “1/10” fatal flaw in early years. Buy a 2020+, and you likely have one of the best daily drivers ever made. Buy a 2018, and you are playing roulette.
Related Guides:
Expert Buying Advice
Target a 2020+ S4 Facelift (B9.5). If buying a 2018-2019, specific inspection of rocker arms is mandatory. Avoid modified examples without service records.