What it means
The Bank 1 Sensor 4 oxygen sensor is responding more slowly than expected. 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 the fourth oxygen sensor on the bank containing cylinder 1, and its placement and monitoring role vary with the exhaust system. This code means the module sees the sensor respond more slowly than expected, which can be caused by an aging sensor, exhaust leak, wiring issue, or an engine condition affecting the exhaust.
Common causes
Most likely first.
- Aged or contaminated oxygen sensor
- Exhaust leak near the sensor
- Damaged wiring or poor connector contact
- Fuel or combustion issue affecting exhaust readings
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Review freeze-frame and Bank 1 Sensor 4 live data to see when the slow response occurred and how the reading changed with engine conditions.
- Inspect the Bank 1 Sensor 4 connector and nearby wiring for heat damage, chafing, corrosion, or loose terminals.
- Check for an exhaust leak near Bank 1 Sensor 4 that could delay or distort the measured exhaust changes.
- Use scan data and the manufacturer's test procedure to assess the sensor's response rather than judging it from a single reading.
- If the sensor circuit is sound, investigate fuel or combustion problems that could make the exhaust readings change abnormally.
Common fixes
- Repair poor connector contact or damaged wiring at Bank 1 Sensor 4.
- Fix an exhaust leak near Bank 1 Sensor 4.
- Correct a confirmed fuel or combustion issue affecting the sensor readings.
- Replace Bank 1 Sensor 4 if it remains slow after circuit and exhaust checks.
Can I keep driving?
A short drive is generally possible if the engine runs normally, though fuel economy and emissions may worsen. Avoid extended driving if rough running or hesitation appears, and address the fault 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.