The Quick Answer above is the generic definition. What follows is the model-specific detail for the Audi models that log P0401.
DTC/P0401·Audi
P0401 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Low SeveritySafe to drive (short-term)Audi
P0401 on a Audi means the engine computer detected too little exhaust gas flowing back through the EGR (Exhaust Gas Recirculation) valve into the intake. That recirculated exhaust dilutes the intake charge to lower nitrogen oxide emissions and combustion temperature. By far the most common cause is carbon buildup clogging the EGR valve or passages, especially on diesels and direct-injection petrol engines. A clean usually costs 80 to 200 EUR.
Typical repair cost, all makes€8 - €550
Connect any standard Bluetooth OBD2 adapter to your Audi and Skanyx tells you what P0401 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0401 mean on a Audi?
Audi A4
2005-2024The A4 shares VW Group TDI and TFSI hardware, so the 2.0 TDI is the most common P0401 vehicle here, with soot building on the valve and the cooler prone to internal leaks. Access is tighter than on the Golf, which raises labour. Direct-injection TFSI petrol engines also build intake carbon that restricts EGR flow over time.
What causes P0401 on a Audi?
Beyond the generic causes listed on the main P0401 page, these are the patterns noted for Audi models:
Audi A4Soot clogging the EGR valve on 2.0 TDI diesel engines
Audi A4EGR cooler internal leak on TDI causing coolant contamination
Audi A4Intake carbon restricting flow on TFSI direct-injection petrol engines
How to diagnose P0401 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0401:
- Read freeze-frame data and confirm P0401 (flow insufficient) rather than P0402 (flow excessive) or an electrical valve code, since the fix differs
- Remove the EGR valve and inspect for heavy carbon deposits on the pintle and seat, a caked valve that will not seat or open cleanly is the most common finding
- Command the valve open with manufacturer-level software (electronic valves; a generic OBD2 reader cannot run this test) or apply vacuum (vacuum-operated), a working valve makes the engine stumble or stall as exhaust floods the intake
- If the valve opens correctly, probe the EGR passages and intake manifold galleries for carbon blockage that restricts flow downstream of the valve
- On DPFE-equipped vehicles (many Fords), test the DPFE sensor and its two rubber hoses for cracks, blockage, or swapped connections that skew the flow reading
- On diesel engines, inspect the EGR cooler for soot blockage or internal coolant leaks, and check vacuum supply hoses on any vacuum-operated system for cracks or disconnection
- Clear the code, drive a full warm-up cycle, and rescan to confirm flow now meets the commanded target before condemning a part
How much does P0401 cost to fix on a Audi? (EUR)
Estimated repair costs for P0401 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.
Codes related to P0401
These codes are often seen alongside P0401 or point to related issues, on any make:
Looking for the full P0401 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0401 guideSkanyx · Audi
Diagnose P0401 on your Audi
Your car logged P0401. Skanyx reads it on any standard Bluetooth OBD2 adapter, tells you whether it is safe to keep driving, and shows the €8-€550 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.
Get Skanyx free