What it means
The Bank 1 Sensor 4 oxygen sensor circuit is reporting a signal below its expected range. 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, with its position depending on the vehicle's exhaust layout. This code means the module sees its signal below the expected voltage range, which can result from a grounded signal wire, poor connection, or sensor fault.
Common causes
Most likely first.
- Signal wire shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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 confirm the low signal and note the engine conditions when it occurred.
- Locate the sensor from service information and inspect its signal wire for chafing, pinching, or contact with ground.
- Check the Bank 1 Sensor 4 connector for corrosion, moisture, loose pins, or poor terminal fit.
- Test the signal circuit for a short to ground and excessive resistance, following the manufacturer's procedure.
- If the wiring and connector pass, test Bank 1 Sensor 4 and its power or heater circuit as applicable.
Common fixes
- Clean and secure corroded or loose Bank 1 Sensor 4 connector terminals.
- Repair the signal wire if it is shorted to ground or chafed through.
- Repair a failed power, ground, or heater connection affecting Bank 1 Sensor 4.
- Replace Bank 1 Sensor 4 if its output remains low after circuit checks.
Can I keep driving?
A brief drive is generally possible if the engine runs smoothly, but the fault can raise fuel consumption and emissions. Avoid extended driving if rough running or hesitation develops, and repair it 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.