What it means
The ECM detects a negative voltage on the signal line of oxygen sensor 3 on bank 2. 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 2 Sensor 3 is the third oxygen-sensor position on the bank 2 exhaust where that configuration is fitted; it is distinct from Bank 2 Sensor 2. The ECM sets this code when Sensor 3 reports a negative signal voltage, which is abnormal for a typical narrow-band sensor and can point to a short or ground-reference offset.
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
- Record freeze-frame data and identify the Bank 2 Sensor 3 channel in live data, comparing it with Bank 2 Sensor 2 and other available oxygen-sensor readings.
- Inspect the Bank 2 Sensor 3 connector and its exhaust-area harness for heat damage, moisture, corrosion, or loose pins.
- Use the wiring diagram to check the Sensor 3 signal circuit for a short to a negative reference and test its ground path for voltage offset.
- Confirm the vehicle is equipped with a Bank 2 Sensor 3 and that the fitted sensor type and wiring match its configuration.
- Test Sensor 3 output and its circuit using the manufacturer's procedure before replacing components.
Common fixes
- Repair damaged Bank 2 Sensor 3 wiring or connector terminals.
- Restore the sensor or ECM ground path if it has an offset.
- Correct an incorrectly wired or incompatible Sensor 3 installation.
- Replace Bank 2 Sensor 3 if it continues to produce a negative signal with wiring and grounds verified.
Can I keep driving?
If the engine runs normally, a short drive is generally possible, though emissions may rise and the vehicle may fail an emissions test. Arrange repair soon and stop if the engine begins stalling or hesitating severely.
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.