What it means
A fault has been detected in the circuit for the Bank 1 Sensor 4 oxygen sensor. 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 identified on the bank containing cylinder 1; its exact position and role depend on the exhaust layout. The control module monitors this sensor's electrical circuit and sets this code when it detects a circuit fault, without specifying whether the signal is low, high, or inactive.
Common causes
Most likely first.
- Oxygen sensor failure
- Damaged sensor wiring or connector
- Blown fuse or poor power/ground connection
- Exhaust leak near the sensor
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Use freeze-frame data and oxygen-sensor live data to see when Bank 1 Sensor 4 faulted and whether its signal is plausible for its location.
- Locate Bank 1 Sensor 4 using vehicle service information and inspect its connector and harness for heat damage, chafing, loose pins, or contamination.
- Check for an exhaust leak near Bank 1 Sensor 4 that could affect its readings.
- Test the sensor circuit's power, ground, and signal wiring, including its fuse where applicable, against the manufacturer's procedure.
- If the circuit is intact, assess Bank 1 Sensor 4 itself and consider related fuel or combustion faults before replacing it.
Common fixes
- Reconnect or clean a poor Bank 1 Sensor 4 connector connection.
- Repair heat-damaged or chafed wiring in the Bank 1 Sensor 4 circuit.
- Repair an exhaust leak near Bank 1 Sensor 4.
- Replace Bank 1 Sensor 4 if testing confirms the sensor has failed.
Can I keep driving?
A short trip is usually possible if the engine runs normally, but fuel use and emissions may increase. Avoid prolonged driving if it runs roughly or hesitates, and address the fault before an emissions inspection.
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.