Can I drive with P0156?

Yes, for short distances. The downstream sensor mainly monitors the bank 2 catalytic converter, so it does not directly change how the engine runs. It is the kind of fault that can get a car rejected at an emissions check, though (rules vary by country), and you may miss a developing converter problem on that bank if you leave it for weeks.

What is Bank 2 Sensor 2?

Most engines with two rows of cylinders, such as V6, V8 and flat-six engines, have a separate catalytic converter and sensors for each row. Bank 1 is the row that contains cylinder 1 and bank 2 is the other one. Sensor 2 is the sensor after the catalytic converter. A few straight-six engines with a split exhaust, such as BMW's N52 and N54, also report cylinders 4-6 as bank 2. A four-cylinder engine with a single exhaust has no bank 2.

What is the difference between P0156 and P0136?

It is the same fault on the other half of the engine. P0136 concerns the downstream sensor on bank 1, P0156 the one on bank 2. If both are stored together, look for something the two sensors share, such as a fuse, the power supply or wiring that runs through the same loom, before replacing two sensors.

Will P0156 fail an emissions test?

It can. Each country writes its own inspection rules and grades defects its own way, but a lit check engine light with a stored emissions code is the kind of fault that gets a car rejected in many inspections, and readiness monitors that have not completed can hold the test up as well. Fix it before the appointment rather than hoping.

How much does it cost to fix P0156 in Europe?

Replacing the downstream sensor at an independent garage typically costs about €90 to €310 in total, depending on the part and how easy the sensor is to reach. An original-equipment sensor fitted at a franchised dealer costs more, up to around €400. On V6 and V8 engines where the bank 2 sensor is hard to reach, labour sits toward the top of the range.

P0156: O2 Sensor Circuit Malfunction (Bank 2, Sensor 2)

Quick Answer

Safe to drive (short-term)

P0156 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.

Severity: Moderate · Emissions
Estimated repair cost: From €45 to €310+, varies by vehicle

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What does P0156 mean?

P0156 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0156 and illuminates the check engine light.

Where it is on the car

Engine
Oxygen sensor before the converter (sensor 1)
Catalytic converter
Oxygen sensor after the converter (sensor 2, or 3 on some cars)
Silencer and tailpipe

This code is for bank 2. V6, V8 and flat engines have two cylinder banks, each with its own converter and sensors; bank 2 is the side without cylinder 1.

What are the symptoms of P0156?

If your vehicle has triggered P0156, you may notice one or more of these symptoms:

Check engine light illuminated
Usually no noticeable change in how the car drives
Slight decrease in fuel economy in some cases
Possible failed emissions test
Catalyst readiness monitor may show as not complete
May appear alongside P0430 if the bank 2 converter is also degrading

What causes P0156?

Here are the most common causes of P0156:

Failing or aged downstream O2 sensor (Bank 2, Sensor 2)
: high
Damaged, corroded or chafed wiring or connector on the bank 2 downstream sensor
: medium
Exhaust leak between the bank 2 catalytic converter and the downstream sensor
: medium
Degrading bank 2 catalytic converter causing sensor signal drift
: low
Oil or coolant contamination of the sensor element
: low

Is it safe to drive with P0156?

Generally yes, for short-term driving. Safe to drive short term. The downstream sensor mainly checks the catalytic converter on bank 2, so fuel mixture control is largely unaffected. It is the sort of fault that gets a car rejected at an emissions check, and ignoring it for weeks can hide a developing converter problem on that bank.

How do you diagnose P0156?

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?

Repair costs for P0156 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Replace downstream O2 sensor (Bank 2, Sensor 2)	€40–€180	€50–€130	€90–€310	Moderate
Repair O2 sensor wiring or connector	€5–€25	€40–€120	€45–€145	Moderate
Fix exhaust leak near downstream sensor	€15–€90	€60–€200	€75–€290	Moderate
Workshop diagnosis (live data and circuit checks)	€0–€0	€60–€120	€60–€120	Professional

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

Oxygen Sensor Replacement Cost

P0156 on specific vehicles

P0156 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0156 on BMW

BMW 3 Series · BMW 5 Series

See BMW-specific causes & cost

P0156 on Mercedes-Benz

Mercedes-Benz E-Class

See Mercedes-Benz-specific causes & cost

P0156 on Audi

Audi A6

See Audi-specific causes & cost

These codes are often seen alongside P0156 or indicate related issues:

Common questions about P0156

Can I drive with P0156?: Yes, for short distances. The downstream sensor mainly monitors the bank 2 catalytic converter, so it does not directly change how the engine runs. It is the kind of fault that can get a car rejected at an emissions check, though (rules vary by country), and you may miss a developing converter problem on that bank if you leave it for weeks.
What is Bank 2 Sensor 2?: Most engines with two rows of cylinders, such as V6, V8 and flat-six engines, have a separate catalytic converter and sensors for each row. Bank 1 is the row that contains cylinder 1 and bank 2 is the other one. Sensor 2 is the sensor after the catalytic converter. A few straight-six engines with a split exhaust, such as BMW's N52 and N54, also report cylinders 4-6 as bank 2. A four-cylinder engine with a single exhaust has no bank 2.
What is the difference between P0156 and P0136?: It is the same fault on the other half of the engine. P0136 concerns the downstream sensor on bank 1, P0156 the one on bank 2. If both are stored together, look for something the two sensors share, such as a fuse, the power supply or wiring that runs through the same loom, before replacing two sensors.
Will P0156 fail an emissions test?: It can. Each country writes its own inspection rules and grades defects its own way, but a lit check engine light with a stored emissions code is the kind of fault that gets a car rejected in many inspections, and readiness monitors that have not completed can hold the test up as well. Fix it before the appointment rather than hoping.
How much does it cost to fix P0156 in Europe?: Replacing the downstream sensor at an independent garage typically costs about €90 to €310 in total, depending on the part and how easy the sensor is to reach. An original-equipment sensor fitted at a franchised dealer costs more, up to around €400. On V6 and V8 engines where the bank 2 sensor is hard to reach, labour sits toward the top of the range.

Read our detailed guides

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