The Quick Answer above is the generic definition. What follows is what is documented for the Audi models that log P0173, checked against manufacturer data and owner reports.
DTC/P0173·Audi
P0173 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Audi
P0173 on a Audi means the ECU has pushed long-term fuel trim on Bank 2 to the limit of its correction range and still cannot maintain the target air-fuel ratio. Because P0173 only affects one bank, it usually points to something specific to Bank 2 (a leak, a degraded sensor, or a dirty injector on that bank) rather than a whole-engine issue like a clogged fuel filter that would affect both banks.
Repair cost on Audi€70 - €420
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Audi A6
2011-2024C7 A6 with the EA837 3.0 TFSI V6 has well-documented Bank 2 fuel trim issues. The supercharger meters air for both banks but Bank 2 sits closer to the bulkhead, where heat soak accelerates O2 sensor aging. P0173 frequently appears before P0171/P0174 on this engine.
What causes P0173 on a Audi?
Beyond the generic causes listed on the main P0173 page, these are the documented Audi-specific patterns:
Audi A6Bank 2 upstream lambda sensor aging on 3.0 TFSI
Audi A6PCV diaphragm leak biasing toward Bank 2
How to diagnose P0173 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0173:
- Read live data: focus on short-term and long-term fuel trim for Bank 2. A long-term trim above +20% or below -20% confirms the bank has been hitting its limits
- Compare Bank 2 trims to Bank 1. If only Bank 2 is out of range, the cause is bank-specific (one injector, one sensor, one manifold gasket section)
- Smoke-test the intake on Bank 2 specifically. On V engines, intake manifold gaskets fail one side at a time as plastic shrinks unevenly
- Swap the upstream sensors between banks and re-check live data. If the high trim follows the sensor, replace it; if it stays on the original bank, focus on mechanical causes
- Inspect for exhaust leaks ahead of the Bank 2 upstream sensor. A small leak can pull fresh air into the exhaust stream and trick the sensor into reading lean
How much does P0173 cost to fix on a Audi? (EUR)
Estimated repair costs for P0173 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 P0173 on Audi
These codes commonly cluster with P0173 on Audi vehicles:
Looking for the full P0173 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0173 guideSkanyx · Audi
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