What it means
O2 Sensor Exhaust Sample Error Bank 1 Sensor 2: the control module has detected this fault condition. (Code P237A)
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 sensor 2 is the oxygen sensor downstream of the catalytic converter on the engine's first bank, where it samples exhaust leaving the catalyst. P237A sets when the control module judges that the exhaust sample reported by this sensor is invalid, which can result from a fouled sensing element or outside air leaking past the sensor seal.
Common causes
Most likely first.
- Sensing element or protective tube fouled with soot, oil or coolant
- Sensor seal or thread 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
- Review freeze-frame and live data for Bank 1 sensor 2 and compare its signal with other oxygen-sensor readings under similar conditions.
- Inspect the sensor's tip and protective tube for soot or signs of oil or coolant contamination.
- Check the sensor threads and seal, and inspect the nearby exhaust for a leak that could dilute the sample.
- Inspect Bank 1 sensor 2's connector and wiring for damage, corrosion, or a poor connection.
- If contamination, leaks, and wiring are ruled out, test Bank 1 sensor 2 and its heater circuit to the manufacturer's specification.
Common fixes
- Repair an exhaust leak at the Bank 1 sensor 2 seal or nearby exhaust joint.
- Repair damaged or corroded wiring and connector terminals for Bank 1 sensor 2.
- Replace Bank 1 sensor 2 if its sensing element is fouled or it fails the manufacturer's test.
- Investigate and repair a confirmed oil or coolant source that is contaminating the sensor.
Can I keep driving?
A short, gentle trip is generally reasonable if the engine runs normally, but prolonged driving can increase emissions and fuel use. Stop if the check-engine light flashes or the engine runs roughly, and arrange diagnosis before an emissions test.
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.