What it means
The Bank 1 Sensor 4 oxygen sensor circuit is reporting a signal above 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 assigned to the bank containing cylinder 1; its exact location varies by exhaust system. This code sets when the module detects a signal above the expected voltage range, which may result from a short to power, a wiring fault, or a sensor problem.
Common causes
Most likely first.
- Signal wire shorted to battery
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Check freeze-frame data and Bank 1 Sensor 4 live data to verify the high reading and capture the conditions when it appeared.
- Find Bank 1 Sensor 4 using service information and inspect its wiring for damage or contact with a battery-voltage feed.
- Inspect the connector for corrosion, displaced pins, or a poor connection that could distort the signal.
- Test the signal circuit for a short to supply voltage and check continuity using the manufacturer's procedure.
- If the circuit is not shorted or open, test Bank 1 Sensor 4 and related power or heater wiring.
Common fixes
- Correct a loose or corroded Bank 1 Sensor 4 connector connection.
- Repair the signal wire if it is contacting a power feed.
- Replace damaged connector terminals or the affected harness section.
- Replace Bank 1 Sensor 4 if circuit tests are satisfactory and the sensor output remains high.
Can I keep driving?
You can usually drive briefly if the engine behaves normally, but fuel use and emissions may increase. Avoid long trips if roughness or hesitation occurs, and fix 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.