What it means
The ECM detects a negative voltage on the signal line of oxygen sensor 3 on bank 1. This is unusual for narrow-band sensors and often indicates a short to a negative reference, ground offset, or a wide-band sensor wired incorrectly.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 3 is a third oxygen sensor on the side containing cylinder 1, fitted on some exhaust systems. The engine control module monitors the sensor's signal circuit and expects its voltage to remain within the valid range for that sensor design. This code sets when the signal is detected below zero, which can indicate a short to a negative reference or a ground offset between the sensor and module.
Common causes
Most likely first.
- Signal wire shorted to negative reference
- Ground offset between sensor and ECM
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Capture freeze-frame data and confirm the vehicle's sensor type and wiring diagram for Bank 1 Sensor 3, because signal circuits differ between sensor designs.
- Check live data for the Bank 1 Sensor 3 signal and compare it with the manufacturer's expected range under the recorded conditions.
- Inspect the sensor connector and harness for chafing, melted insulation, corrosion, or contact with a negative reference wire.
- Check sensor and module grounds for poor connections or voltage offset using the manufacturer's diagnostic procedure.
- Test the signal circuit for a short to negative reference and verify wiring continuity before replacing the sensor or module.
Common fixes
- Repair chafed or shorted Bank 1 Sensor 3 signal wiring.
- Clean and secure the sensor or module ground connection if testing shows a ground offset.
- Repair a damaged connector or terminal that is bridging the signal to a negative reference.
- Replace Bank 1 Sensor 3 only if its signal remains incorrect with sound wiring and grounds.
Can I keep driving?
The vehicle may remain drivable if it runs normally, but use only short, gentle trips until the circuit fault is diagnosed. An invalid oxygen reading can disrupt mixture or emissions monitoring, increasing fuel use and emissions.
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.