What it means
O2 Sensor Exhaust Sample Error Bank 2 Sensor 2: the control module has detected this fault condition. (Code P237B)
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 2 Sensor 2 is the oxygen sensor downstream of the catalytic converter on the engine's second cylinder bank. The control module evaluates this sensor's exhaust sample to monitor downstream oxygen content. This code sets when the sample appears unreliable, such as when the sensing element or protective tube is fouled or a leaking sensor seal lets outside air dilute the exhaust.
Common causes
Most likely first.
- Sensing element or protective tube fouled
- Sensor seal leaks - bypass air dilutes sample
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Record freeze-frame data and compare Bank 2 Sensor 2 readings with the upstream sensor and the other bank under similar conditions to see when the sample becomes implausible.
- Inspect the downstream Bank 2 sensor tip and protective tube for soot, deposits, damage, or contamination.
- Check that Bank 2 Sensor 2 is seated correctly and inspect its seal and nearby exhaust joints for leaks that could admit outside air.
- Inspect the sensor connector and wiring for damage, loose pins, corrosion, or contact with hot exhaust parts.
- If the sample remains suspect, test the sensor response and circuit using the vehicle's service information before replacing the sensor.
Common fixes
- Repair an exhaust leak or replace a leaking Bank 2 Sensor 2 seal.
- Repair damaged or loose wiring and connector terminals at Bank 2 Sensor 2.
- Replace Bank 2 Sensor 2 if its sensing element is contaminated or its response fails the specified test.
- Repair an exhaust leak near the sensor that is diluting its sample.
Can I keep driving?
Usually, short trips are possible if the engine runs normally, but arrange diagnosis soon because fuel use and emissions can increase. Avoid extended driving if rough running or hesitation worsens.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.