A Guide to the 2008-2013 Audi S5 Secondary Air Injection Control Valve
Understanding the check engine light and emissions faults related to your S5's secondary air system.
- P0491 and P0492 codes on an S5 are most often caused by clogged carbon ports, not a bad valve.
- Driving with a faulty SAI system is safe but will cause an automatic emissions test failure.
- Diagnose the system properly before buying parts; you may need an expensive carbon cleaning service instead of a new valve.
- If the valve is confirmed bad, Hella is a premium aftermarket choice, while Dorman offers a standard replacement.
Diagnosing a Failing Secondary Air System
When your 2008-2013 Audi S5 has a problem with its secondary air injection system, the first and most obvious symptom is a check engine light on your dashboard. This is often accompanied by fault codes P0491 🎬 Watch: A deep dive into diagnosing these specific fault codes. (Insufficient Flow, Bank 1) and P0492 (Insufficient Flow, Bank 2) stored in the engine's computer. While a faulty control valve can be the cause, it is critical to diagnose the system correctly, as other issues are very common with these vehicles.
The Real Issue: Carbon Buildup
For the 4.2L V8 and 3.0L V6 engines used in this S5 generation, the most common cause of P0491 and P0492 codes is not a failed valve or pump, but severe carbon buildup inside the cylinder heads. Over time, tiny air passages that lead to the exhaust ports become clogged with carbon. When this happens, air from the pump cannot get through, which triggers the insufficient flow codes, even if the pump and valves are working perfectly. Replacing the valves without addressing clogged ports will not fix the problem.
Choosing the Right Aftermarket Part
If you have confirmed the control valve itself is faulty (for example, it leaks vacuum or is stuck open), several aftermarket options are available. Choosing the right one depends on your budget and quality expectations.
- Premium Aftermarket (Hella): Hella is often a supplier of original parts to Audi and other German manufacturers. Choosing a Hella valve generally provides OEM-level fit and quality for a lower price than a part from the dealer.
- Standard Aftermarket (Dorman): Dorman is a major aftermarket manufacturer that produces direct replacement parts. These parts are designed to match the original's function and are widely available. While generally reliable, it's always wise to confirm fitment before installation.
- Economy Aftermarket (Vaico): Vaico offers a budget-friendly alternative. These parts can be a good choice for repairs on a tight budget, but may not offer the same longevity as premium brands.
Pro Tip: Before ordering a new valve, test the old one. A simple hand-held vacuum pump can be used to see if the valve's diaphragm holds a vacuum and opens correctly. Also, check the vacuum lines running to the valves, as they can become brittle and crack over time, causing similar symptoms.
Cost of Replacing an Audi S5 Secondary Air Valve
| Part Type | Estimated Cost |
|---|---|
| New OEM | $450+ (per valve) |
| New Aftermarket | $14 - $148 |
| Shop Labor | $250 - $500 (valve replacement only) |
| Carbon Cleaning Service | $1500 - $3000+ |
Cost estimates are approximate and can vary based on your location and the specific repair shop. The high cost of carbon cleaning is due to the extensive labor required.
Frequently Asked Questions
What is a "combi valve"?
Combi valve, or combination valve, is another name for the Secondary Air Injection Control Valve on your Audi. The 4.2L V8 engine has two of them, one on the back of each cylinder head.
🎬 See this walkthrough on how to replace the combi valves.Can I just clean the control valve?
If the valve is sticking due to light carbon deposits, cleaning it might be a temporary solution. However, the valves are often replaced because the internal rubber diaphragm fails, which cannot be repaired. The more important cleaning is for the air passages inside the cylinder head, which is a much more involved job.
What happens if I ignore the P0491/P0492 codes?
Your car will drive normally. The secondary air system does not affect engine performance or reliability after the first minute of startup. 🎬 Watch: How the secondary air injection system actually works. However, the check engine light will stay on, and your vehicle will automatically fail any state emissions inspection.
Is there a recall for this issue?
No, there are no active recalls from the NHTSA for the secondary air injection system on the 2008-2013 Audi S5. Audi did issue a Technical Service Bulletin (TSB) and a warranty extension for some models due to the carbon buildup issue, but this may have expired.
Helpful Videos
Technical Specifications
OEM Part Numbers: 078131101AG 078131102T
The 4.2L V8 engine uses two vacuum-actuated combination (combi) valves, one for each cylinder bank.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
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