A failing Audi PCV valve is the 3.0T's favorite way to ruin a quiet morning: a high-pitched whistle at idle, a stumble at the lights, a lean code, and an oil cap that seems glued on by vacuum. The valve itself is not expensive. The problem is where Audi put it, down in the engine valley under the supercharger, wrapped in plastic that heat slowly turns brittle. The fix is simple once you know which part number your engine takes, starting with the genuine Hengst 06E103547AH Audi PCV valve for most later Gen 1 3.0T cars.
Below: how the system works, the symptoms, a test sequence that proves the diagnosis, the right Hengst OE valve for your engine, and when a billet PCV relocation beats buying the same plastic again.
What the Audi PCV Valve Does
Every engine pushes some combustion gas past the piston rings. That blow-by pressurizes the crankcase. The positive crankcase ventilation (PCV) system separates oil mist from those gases and meters them back into the intake so they burn instead of venting to atmosphere. On the EA837 3.0T, the PCV valve is an oil separator with a pressure-regulating rubber diaphragm, sitting at the back of the valley and feeding the intake through plastic pipes.
When the diaphragm tears or hardens, the valve stops regulating. The engine sees unmetered air (a vacuum leak) or the crankcase builds pressure and starts pushing oil past seals. Either way, the ECU notices before you do.
Audi PCV Valve Symptoms on the 3.0T
- ✅ Whistling, squealing or howling from the back of the engine, loudest at idle.
- ✅ Rough, hunting or surging idle, sometimes stalling.
- ✅ Lean codes like P0171/P0174 and idle speed codes like P0507.
- ✅ Strong suction on the oil filler cap with the engine running.
- ✅ Rising oil consumption, oil in the intake tract, or new oil leaks at seals.
- ✅ Misfire codes caused by unmetered air.
Any one of these can also come from a cracked PCV pipe, a leaking intake manifold gasket, or a bad check valve. That is why the test sequence matters.
How to Diagnose a Bad PCV Valve (Before Buying Parts)
The oil cap test is a clue, not a verdict. Use this order:
- Scan and log fuel trims. Healthy idle trims sit near zero. Large positive trims at idle that improve with RPM point to a vacuum leak.
- Listen with a hose or stethoscope. A torn diaphragm usually whistles from the rear of the valley.
- Smoke test the intake. Smoke escaping at the PCV, a cracked pipe, or the manifold gaskets tells you exactly where the leak lives.
- Check the PCV pipes and hoses. Old plastic cracks at the elbows. Our PCV breather hose guide covers the 3.0T pipes by part number.
- Check the check valves. A stuck check valve can mimic PCV failure. See our vacuum check valve guide.
If the smoke comes out at the valve body, you have your answer. If trims still look off after that, rule out the MAF with our Audi MAF sensor guide.
Which Audi PCV Valve Do You Need? Hengst OE Part Numbers
Hengst is an OE supplier for this valve, so a genuine Hengst unit is the factory part without the dealer box and without the Audi Tax. The catch: there are three part numbers, and they are not interchangeable. Always confirm with your VIN or the number stamped on your old valve, because model-year cutovers overlap.
| Hengst part number | Engine | Typical applications (confirm by VIN) | Price |
|---|---|---|---|
| 06E103547AC | Early Gen 1 EA837 | 2010-2012 B8 S4/S5, 2009-2012 C6 A6, 2009-2014 4L Q7 | $114.99 |
| 06E103547AH | Later Gen 1 EA837 | 2013-2016 B8.5 S4, B8/B8.5 S5, B8.5 Q5 3.0T and SQ5, 2012-2015 C7 A6/A7, D4 A8 3.0T, 7P Touareg | $149.99 |
| 06E103547AF | Gen 2 CREC | Later C7 A6/A7, D4 A8 and Q7 with the CREC engine | $199.99 |
Not sure if you have Gen 1 or CREC? Our Audi V6 supercharged engine guide explains the difference and where to find the engine code.
OE Replacement vs PCV Relocation vs Dealer
You have three honest options. Replace with the genuine OE valve and expect the same service life as the original. Pay dealer pricing for the identical part plus Audi Tax labor. Or, if you are tracking the car, running more boost, or just tired of the plastic, relocate the PCV with billet parts that live outside the heat of the valley.
| Hengst OE valve | Vorsprung billet relocation | Dealer/OEM | |
|---|---|---|---|
| What it is | Factory-spec valve from the OE supplier | Billet housing adapter with AN ports plus a GLT diaphragm | Same valve in an Audi box |
| Material | OE plastic and rubber | Billet aluminum, Viton GLT diaphragm | OE plastic and rubber |
| Serviceability | Supercharger off to replace | Relocated, easier to service later | Supercharger off to replace |
| Best for | Stock daily drivers | Tuned, tracked or long-term cars | Warranty work |
| Price | $114.99 to $199.99 | Adapter $74.99, diaphragm $19.99 | Dealer pricing |
For a stock car, the genuine Hengst Audi PCV valve 06E103547AH is the straightforward fix.
Shop the Hengst Audi PCV Valve 06E103547AH, $149.99
✅ Genuine Hengst OE-supplier valves ✅ Fitment checked by engine code and VIN on request ✅ Fast US shipping
Billet PCV Relocation Parts
- ✅ Billet PCV Housing Adapter ($74.99): replaces the fragile lower plastic section of the factory housing with machined aluminum and adds threaded ports for AN fittings. Bolt-on, no cutting. Includes a battery location mount confirmed for B8/B8.5 S4 and S5.
- ✅ GLT TruSeal PCV Valve Diaphragm Upgrade ($19.99): Viton GLT diaphragm rated -40°F to +400°F. On the 3.0T it is a relocation-build component, not a bolt-in for the factory location.
- ✅ Billet PCV Breather Quick Connect, 19mm to 10AN ($44.99-$49.99) for clean AN routing off the valve cover.
- ✅ PCV pipe 06E103207AP ($64.99) and PCV pipe 06E103207P / AM ($34.99) if your stock pipes are cracked.
Relocation involves routing and hose choices, so talk to us before you build one. Browse the full range in our OEM+ upgrades and fixes collection.
Installation Notes
- ✅ On the EA837 the supercharger comes off to reach the PCV valve. Plan a full valley service rather than a single part.
- ✅ Replace the intake manifold gaskets when the supercharger comes off. The GLT TruSeal intake manifold gasket set ($49.99) is the upgrade.
- ✅ Inspect the thermostat housing, coolant pipes and PCV pipes while you are there. Our oil filter housing gasket guide and oil filter housing gasket replacement steps cover the other common valley leak.
- ✅ Clear codes and re-check fuel trims after a few drives to confirm the leak is gone.
Audi PCV Valve FAQ
What are the symptoms of a bad Audi PCV valve?
A whistle or squeal at idle, rough or surging idle, lean codes like P0171, idle speed codes like P0507, strong vacuum on the oil cap, and rising oil consumption or new oil leaks.
Where is the PCV valve on an Audi 3.0T?
At the back of the engine valley, under the supercharger. The supercharger has to come off to replace it on the EA837.
Which PCV valve fits my Audi 3.0T?
06E103547AC fits early Gen 1 engines, 06E103547AH fits later Gen 1 engines, and 06E103547AF fits Gen 2 CREC engines. Confirm with your VIN or the part number on your old valve.
Is a Hengst PCV valve the same as the Audi part?
Hengst is an OE supplier for this valve. The genuine Hengst unit is built to the same factory part number without dealer pricing.
Can I drive with a bad Audi PCV valve?
Short term, usually yes, but a torn diaphragm causes a vacuum leak, lean running and oil consumption. Left alone it can foul the intake and push oil past seals, so fix it soon.
What is a PCV relocation on the 3.0T?
It moves crankcase ventilation duties away from the hot valley using a billet housing adapter, AN fittings and a separate diaphragm, which makes future service easier. It suits tuned and tracked cars.
How often should the Audi PCV valve be replaced?
There is no fixed interval. Replace it when symptoms appear, or preventively whenever the supercharger comes off for other valley work.
Bottom Line on the Audi PCV Valve
A whistling, lean-running 3.0T usually has a tired Audi PCV valve under the supercharger. Prove it with trims and a smoke test, match the Hengst part number to your engine, and replace the valley plastics while you are in there. For stock cars, the genuine Hengst 06E103547AH PCV valve (or the AC or AF version for your engine) gets you back to factory behavior. For tuned cars, the billet adapter and GLT diaphragm take the problem out of the valley for good.
Shop the Hengst Audi PCV Valve 06E103547AH, $149.99
Drive the difference. Drive Vorsprung.
Prices checked September 25, 2026 and subject to change.
