The Quick Answer above is the generic definition. What follows is the model-specific detail for the Audi models that log P0156.
DTC/P0156·Audi
P0156 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Audi
P0156 on a Audi means the engine computer is getting a signal from the Bank 2 downstream oxygen sensor (after the catalytic converter, Sensor 2) that is outside its expected range or does not make sense. Bank 2 is the half of the engine that does not contain cylinder 1, so this code only appears on engines whose exhaust is monitored in two separate halves: most V6 and V8 engines, flat-six engines and a few straight-sixes with a split exhaust. The sensor's job is to check how well the bank 2 catalytic converter is cleaning the exhaust, and the usual causes are the sensor itself, its wiring or an exhaust leak.
Typical repair cost, all makes€45 - €310
Connect any standard Bluetooth OBD2 adapter to your Audi and Skanyx tells you what P0156 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
2004-2009The 3.2 V6 FSI in the C6-generation A6 has four oxygen sensors: two ahead of the catalytic converters and two behind them. In Audi's wiring diagrams the bank 2 post-catalyst sensor is G131, which is the name to look for in a workshop manual or when ordering the part.
What causes P0156 on a Audi?
Beyond the generic causes listed on the main P0156 page, these are the patterns noted for Audi models:
Audi A6Aged G131 post-catalyst sensor on bank 2
Audi A6Wiring or connector damage on the G131 circuit
How to diagnose P0156 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0156:
- Confirm which sensor the code means before buying parts: Bank 2 is the cylinder bank that does not contain cylinder 1, and Sensor 2 is the one after the catalytic converter. Check the cylinder numbering for your engine in the service information, because the side of the car bank 2 sits on is not the same on every engine
- Read freeze frame data to capture the engine conditions when the code was set (RPM, coolant temp, load) and note companion codes such as P0430, P0157-P0161 or the bank 1 equivalent P0136
- Inspect the exhaust between the bank 2 catalytic converter and the downstream sensor for cracks, loose clamps or leaking gaskets
- Inspect the Bank 2 Sensor 2 connector and wiring for corrosion, heat damage or chafing against the exhaust or heat shields
- With the engine warm, view live data for both downstream sensors. A healthy downstream sensor holds a relatively flat voltage around 0.6-0.8V rather than switching rapidly like the upstream sensor, and the bank 1 and bank 2 downstream readings should behave in a similar way
- On engines with a switching (narrowband) upstream sensor, a bank 2 downstream sensor that copies the switching of its upstream sensor means the bank 2 converter is likely failing. If it is erratic or stuck while the bank 1 downstream sensor looks normal, the sensor or its wiring is the likely fault
How much does P0156 cost to fix on a Audi? (EUR)
Estimated repair costs for P0156 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 P0156
These codes are often seen alongside P0156 or point to related issues, on any make:
Looking for the full P0156 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0156 guideSkanyx · Audi
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Your car logged P0156. Skanyx reads it on any standard Bluetooth OBD2 adapter, tells you whether it is safe to keep driving, and shows the €45-€310 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.
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