What it means
The optional third oxygen sensor on bank 1 (typically downstream of a second catalyst) returns implausible values during long-term monitoring.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 3 is a third oxygen sensor on the side containing cylinder 1, fitted on some exhaust systems, often after a second catalyst stage. The control module checks its signal over time for plausible behavior at that downstream location. This code sets when the long-term signal falls outside the expected range, which may result from sensor aging or a loose mounting that dampens the signal.
Common causes
Most likely first.
- Sensor aging
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Use a scan tool to save freeze-frame data and confirm which sensor the vehicle identifies as Bank 1 Sensor 3, since not every exhaust system has a third sensor.
- Check live data for Bank 1 Sensor 3 under the temperature and driving conditions described by the manufacturer's diagnostic procedure.
- Inspect the third sensor's mounting, connector, and wiring for looseness, corrosion, heat damage, or contamination.
- Check the exhaust joints ahead of this sensor for leaks that could affect its reading.
- If mounting, wiring, and exhaust are sound, test the sensor circuit and response against the manufacturer's specification.
Common fixes
- Secure a loose Bank 1 Sensor 3 mounting and repair its connector or wiring as needed.
- Repair an exhaust leak upstream of the sensor.
- Correct any identified contamination source.
- Replace Bank 1 Sensor 3 if it fails the specified response test.
Can I keep driving?
If the vehicle runs normally, limited driving is generally possible while you arrange diagnosis. The fault can increase emissions and cause a failed emissions test; address rough running promptly to reduce the risk of exhaust-system damage.
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.