What it means
The fourth oxygen sensor on bank 2 returns values outside the expected long-term performance window during plausibility checks.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 2 Sensor 4 is a fourth oxygen sensor on the side opposite the bank containing cylinder 1, used on some multi-stage exhaust systems. The control module monitors this far-downstream signal over time for plausible performance. This code sets when the signal is outside its expected long-term window, which can be caused by sensor aging or a loose sensor mounting that dampens the reading.
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
- Record freeze-frame data and verify the vehicle has Bank 2 Sensor 4, as a fourth sensor is not fitted to every exhaust system.
- Review live data for Bank 2 Sensor 4 under the manufacturer's required monitoring conditions.
- Inspect its mounting, connector, and wiring along the exhaust for looseness, corrosion, or heat damage.
- Check for exhaust leaks upstream of the fourth sensor that might affect the oxygen reading.
- If the mounting and circuit are intact, test Bank 2 Sensor 4 response against the manufacturer's specification.
Common fixes
- Secure the Bank 2 Sensor 4 mounting if loose.
- Repair a damaged wire or connector at the sensor.
- Repair an upstream exhaust leak.
- Replace Bank 2 Sensor 4 if it fails the specified signal test.
Can I keep driving?
If the vehicle drives normally, limited trips are generally possible while arranging diagnosis. The fault can increase emissions and result in a failed emissions test, so do not ignore it.
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.