The Quick Answer above is the generic definition. What follows is what is documented for the Audi models that log P0171, checked against manufacturer data and owner reports.
DTC/P0171·Audi
P0171 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Audi
P0171 on a Audi means the air-fuel mixture on Bank 1 (the cylinder bank with cylinder 1) is too lean: too much air or too little fuel. The ECU keeps adding fuel to hit the 14.7:1 target ratio, but it has run out of room to compensate, so long-term fuel trim climbs past about +15% and the light comes on. The single most common cause is unmetered air entering after the airflow sensor, usually a vacuum or intake leak. Most fixes land between 100 and 350 EUR.
Repair cost on Audi€30 - €700
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Audi A4
2008-2024The A4 shares the EA888 family with the Golf, so the PCV and oil separator diaphragm is the prime P0171 suspect and tends to fail again if a cheap aftermarket part is fitted. On the 2.0 TFSI also inspect the intake manifold gasket and the charge pipe, and confirm fuel pressure, since the high-pressure fuel system can lean out under load when the pump or cam follower is worn.
What causes P0171 on a Audi?
Beyond the generic causes listed on the main P0171 page, these are the documented Audi-specific patterns:
Audi A4PCV and oil separator diaphragm failure on the EA888 2.0 TFSI
Audi A4Intake manifold gasket leaks and charge pipe cracks
How to diagnose P0171 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0171:
- Read short-term and long-term fuel trims with a scan tool. Long-term fuel trim above roughly +15% at idle confirms the lean condition, and if it improves at higher RPM the leak is unmetered air at idle
- Smoke-test the intake, or spray brake cleaner or carb cleaner around the intake manifold gasket, vacuum hoses, and PCV connections. A momentary RPM change pinpoints the leak
- Inspect and clean the MAF sensor with dedicated MAF cleaner, never touching the sensor element, then recheck fuel trims
- Check fuel pressure at the rail with a gauge and compare to the manufacturer specification, watching for pressure drop under load that points to a weak pump or clogged filter
- Inspect the PCV valve, oil separator, and their hoses for cracks, splits, or disconnection
- Check for an exhaust leak just before the upstream O2 sensor, which can fool the sensor into a false lean reading
- Compare Bank 1 and Bank 2 trims on V engines. If both banks read lean, suspect a shared cause such as the MAF, fuel supply, or a leak before the throttle body
How much does P0171 cost to fix on a Audi? (EUR)
Estimated repair costs for P0171 in EUR, compiled across makes. Expect Audi parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0171 on Audi
These codes commonly cluster with P0171 on Audi vehicles:
Looking for the full P0171 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0171 guideSkanyx · Audi
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