The Quick Answer above is the generic definition. What follows is what is documented for the Audi models that log P0431, checked against manufacturer data and owner reports.
DTC/P0431·Audi
P0431 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Audi
P0431 on a Audi means the warm-up catalyst (the small pre-cat closest to the exhaust manifold) on Bank 2 is not heating up fast enough or converting cold-start emissions efficiently. Bank 2 is the cylinder bank that does not contain cylinder 1, which only exists on V6, V8, V10, V12, and some flat engine layouts.
Repair cost on Audi€125 - €1720
Connect any standard Bluetooth OBD2 adapter to your Audi and Skanyx tells you what P0431 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
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Audi A6
2005-2024On the Audi A6 3.0 TFSI (EA837 supercharged V6) and 3.0 TDI V6, P0431 points to the Bank 2 (driver side) pre-cat. The EA837 is known for carbon buildup on intake valves that causes uneven combustion and accelerates Bank 2 wear due to cylinder-4 typically running slightly richer than cylinder-1. A walnut blast service before pre-cat replacement is strongly recommended.
What causes P0431 on a Audi?
Beyond the generic causes listed on the main P0431 page, these are the documented Audi-specific patterns:
Audi A6EA837 cylinder-4 enrichment accelerating Bank 2 pre-cat wear
Audi A6Carbon-fouled intake valves causing uneven combustion on Bank 2
How to diagnose P0431 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0431:
- Confirm the engine actually has two banks. If you see P0431 on an inline-4, suspect a scan tool error or a wiring fault
- Read freeze frame data and verify coolant temperature was below 40°C when the code set, which is typical of cold-start warm-up cat faults
- Scan for Bank 2 misfire codes (P0305 to P0308) and address those before condemning the pre-cat
- Graph Bank 2 upstream and downstream O2 sensors during cold start. The downstream sensor should stabilise near 0.45 V within 60 to 90 seconds on a healthy pre-cat
- Compare Bank 1 and Bank 2 downstream O2 sensor traces. If only Bank 2 is showing oscillation, the Bank 2 pre-cat is the likely culprit
How much does P0431 cost to fix on a Audi? (EUR)
Estimated repair costs for P0431 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 P0431 on Audi
These codes commonly cluster with P0431 on Audi vehicles:
Looking for the full P0431 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0431 guideSkanyx · Audi
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