What it means
The control module detects a low signal in the negative-current control circuit for the Bank 1 Sensor 1 oxygen sensor. This indicates a circuit signal fault; it does not by itself identify the failed part.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 1 is the upstream wide-band oxygen sensor, and its negative-current control line helps provide the reference used to measure the exhaust air-fuel mixture. The control module sets this code when the Vs− signal is lower than expected; a short to ground, an internal sensor return fault, or a poor connection can cause it.
Common causes
Most likely first.
- Vs negative line shorted to ground
- Nernst cell return open inside sensor
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Review freeze-frame data and fuel-trim or oxygen-sensor codes to establish when Bank 1 Sensor 1’s Vs− signal went low.
- Inspect the Bank 1 Sensor 1 connector and harness for corrosion, loose pins, or wiring rubbed through to ground.
- Use the wiring diagram to identify the Vs− wire and check for a short to ground with the sensor disconnected as specified by the manufacturer.
- Check the sensor return and connector terminals for an open or high-resistance connection using the manufacturer’s procedure.
- If the wiring and connections pass, test Bank 1 Sensor 1’s internal Nernst-cell return and replace the sensor only if confirmed faulty.
Common fixes
- Clean and secure corroded or loose Bank 1 Sensor 1 connector terminals.
- Repair a Vs− wire shorted to ground or replace the damaged harness section.
- Replace Bank 1 Sensor 1 if its internal Nernst-cell return is faulty.
- Repair a confirmed module-side circuit fault.
Can I keep driving?
The engine may remain drivable, but the module may receive an unreliable upstream mixture reading, increasing fuel use and emissions. Avoid extended driving if the engine runs roughly or hesitates.
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.