A Guide to the 2008-2017 Audi A4 Secondary Air Injection Control Valve
Having trouble with a Check Engine Light? Learn about your A4's secondary air injection valve and how to choose the right replacement.
- A bad valve will cause a Check Engine Light with code P0411 and will make your A4 fail an emissions test.
- A loud whining noise on cold starts often means the air pump is also failing due to a bad valve.
- Always inspect the air pump and hoses when replacing the valve to avoid repeat failures.
- An aftermarket valve from a quality brand like Hella or Vemo is a cost-effective and reliable alternative to expensive OEM parts.
Symptoms of a Failing Air Injection Valve
A bad secondary air injection control valve on your 2008-2017 Audi A4 will almost always let you know there's a problem. While it won't stop you from driving, it will cause your car to fail an emissions test. Here are the most common signs of failure:
- Check Engine Light: This is the most frequent symptom. Your A4's computer monitors the air injection system and will trigger a light if it detects a problem. You will likely see fault code P0411 (Secondary Air Injection System Incorrect Flow Detected). Other related codes include P0491 and P0492, which point to insufficient flow.
- Loud Whining Noise on Cold Start: A failing control valve can get stuck open, allowing hot exhaust gases and moisture to flow backward into the secondary air pump. This damages the pump's bearings, causing a loud noise like a vacuum cleaner for the first minute after starting the engine. If you hear this, the pump is likely failing due to a bad valve.
- Failed Emissions Test: The secondary air injection system's only purpose is to reduce emissions on startup. If the valve or any other part of the system is not working correctly, your vehicle will not pass an emissions inspection.
Choosing the Right Aftermarket Part
When replacing the secondary air injection valve, you have a choice between Original Equipment (OEM) and aftermarket parts. For a vehicle like the B8 generation A4, high-quality aftermarket parts offer a reliable repair without the high cost of an OEM part from the dealer. The key is to choose a reputable brand.
Based on our inventory, here's a look at the available brands:
- Hella: A well-respected German brand that often manufactures parts for Audi and other European carmakers. Hella is known for its quality and is a solid choice that balances cost and reliability.
- Vemo: Vemo is another German brand that produces a wide range of aftermarket parts. It is often considered a good quality alternative to OEM parts.
- Vaico: Vaico parts are also German-made and are known for providing good value. They are a viable option for budget-conscious repairs.
Pro Tip: If you are replacing the control valve, it is critical to inspect the secondary air pump and all associated hoses. If the valve failed and allowed moisture into the pump, the pump will likely fail soon after. Replacing both the valve and a damaged pump at the same time can save you from doing the job twice.
Known Issues for the 2008-2017 Audi A4
While there are no specific recalls from the NHTSA for the secondary air injection valve on this generation of A4, Audi has issued Technical Service Bulletins (TSBs) for related problems. One common issue is the clogging of secondary air ports in the cylinder head with carbon buildup. This can cause "Insufficient Flow" codes (P0491/P0492) even if the pump and valve are working correctly. The repair involves a special cleaning procedure.
Replacement Cost
The cost to replace the secondary air injection control valve can vary significantly between doing it yourself and having a shop perform the work. The part itself is relatively affordable, but labor costs can be high.
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Valve | $23.80 - $87.48 |
| New OEM Valve | $450+ |
| Shop Labor | $119 - $175 |
| Total Professional Replacement (OEM Part) | $745 - $901+ |
Frequently Asked Questions
Can I clean a secondary air injection valve?
While some owners attempt to clean the valve, it is often not a permanent solution. The internal diaphragm can fail or the valve body can become warped, which cleaning won't fix. Given the relatively low cost of an aftermarket part and the labor involved to access it, replacement is the recommended repair.
What is the difference between a control valve and a check valve?
On the Audi A4, the secondary air injection control valve is also called a "combi valve" because it combines the function of a control valve (opening and closing on command) and a check valve (preventing exhaust from flowing backward). So, for this vehicle, they are the same part.
What happens if I don't replace a bad air injection valve?
Your car will still drive, but the check engine light will stay on, and you will fail any emissions test. More importantly, a valve stuck open can allow moisture to destroy the much more expensive secondary air pump, leading to a costlier repair down the road.
Is the secondary air injection system the same as the EGR system?
No, they are different systems. The secondary air injection (SAI) system adds fresh air to the exhaust during cold starts. The Exhaust Gas Recirculation (EGR) system routes a small amount of exhaust gas back into the engine's cylinders to reduce NOx emissions under certain operating conditions.
Technical Specifications
OEM Part Numbers: 06F131102G 078131101AG 078131102T
Also known as a Combi Valve. This is a vacuum-actuated valve that controls the flow of fresh air into the exhaust manifold during cold starts.
We Have This Part in Stock
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.
- Audi A4: