What it means
The Bank 1 Sensor 4 oxygen sensor signal is biased or stuck lean. Sensor location and function vary with the exhaust system.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 4 is a downstream oxygen sensor at the fourth designated sensor position on Bank 1; its location and role depend on the exhaust layout. The control module monitors its signal and sets P01F6 when the reading remains lean or is biased lean when operating conditions call for a different response.
Common causes
Most likely first.
- Oxygen sensor failure or contamination
- Exhaust leak near the sensor
- Damaged wiring or poor connector contact
- Engine running lean from an air or fuel delivery issue
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 record freeze-frame data and compare Bank 1 Sensor 4 live data with the other oxygen sensors under similar operating conditions.
- Inspect the exhaust around Sensor 4 for leaks that could draw in oxygen and make its reading appear lean.
- Check the Sensor 4 connector and wiring for corrosion, loose pins, heat damage, or chafing.
- Inspect the sensor for contamination or damage and check its signal circuit, power, and ground against the manufacturer's specification.
- If the sensor circuit checks out, investigate engine air leaks and fuel delivery problems that could cause a genuinely lean mixture.
Common fixes
- Repair an exhaust leak near Bank 1 Sensor 4.
- Repair damaged wiring or clean and secure the sensor connector.
- Correct an intake air leak or fuel delivery problem causing a lean condition.
- Replace a contaminated or failed Bank 1 Sensor 4 oxygen sensor.
Can I keep driving?
If the engine runs smoothly, you can usually drive gently for a short time, but arrange diagnosis soon because the lean-biased reading can impair emissions control and fuel economy. Stop if it begins running roughly or loses power.
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.