P0431 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.
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€163 - €2236
What does P0431 mean on a Audi?
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 Audi-specific patterns we see most often:
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 on a Audi (Audi parts and labour typically run 30% above the average for this code).
Prices estimated as of May 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:
FAQ: P0431 on Audi
What engines have a Bank 2, and which do not?
Bank 2 only exists on engines with multiple cylinder banks: V6, V8, V10, V12, and some boxer or flat layouts. Inline-4, inline-5, and inline-6 engines have only one bank, so codes P0431 through P0434 should never appear on those. If you see P0431 on an inline-4, the scan tool reading is almost certainly wrong.
Why does Bank 2 wear faster than Bank 1 on some engines?
On many V6 and V8 layouts, the Bank 2 exhaust runs closer to the firewall or has tighter packaging, which traps heat and accelerates substrate aging. On other engines, fuel-trim differences between banks (caused by intake manifold geometry or injector wear) lead to one bank running slightly richer and ageing the catalyst faster.
Can I just replace the Bank 2 pre-cat, or do I need to replace both?
If only P0431 is set and Bank 1 is healthy, you can replace just the Bank 2 unit. However, if both banks are at similar mileage (typical), the Bank 1 pre-cat is often within months of failing too. Many owners replace both at the same time to consolidate labour cost.
Will P0431 alone cause a periodic technical inspection failure?
Yes. The check engine light alone is an automatic fail in most EU periodic inspections (TÜV, ITV, SKP, TA), regardless of which bank is affected. P0431 must be resolved and the readiness monitors must be set before retesting.
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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