What it means
The ECM detects a negative voltage on the signal line of oxygen sensor 1 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 1 is the upstream oxygen sensor ahead of the catalytic converter on the side opposite the bank containing cylinder 1. Its signal circuit is monitored by the engine control module during fuel control. This code sets when that signal is detected below zero, an abnormal condition that can result from a short to a negative reference or a ground offset in the Bank 2 sensor circuit.
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
- Save freeze-frame data and confirm the sensor design and Bank 2 Sensor 1 wiring from the vehicle's service information before interpreting the signal.
- Use live data to check whether the Bank 2 Sensor 1 signal falls below its valid range under the recorded operating conditions.
- Inspect the upstream sensor's connector and harness for abrasion, melted insulation, corrosion, or contact with a negative reference wire.
- Check Bank 2 Sensor 1 and module grounds for poor connections or voltage offset using the manufacturer's procedure.
- Test the signal wire for a short to negative reference and verify circuit continuity before considering sensor replacement.
Common fixes
- Repair a shorted or chafed Bank 2 Sensor 1 signal wire.
- Clean and secure a poor sensor or module ground if measurements confirm an offset.
- Repair damaged connector terminals that could bridge the signal circuit.
- Replace Bank 2 Sensor 1 if it fails testing after wiring and grounds are verified.
Can I keep driving?
If the engine runs normally, drive only as needed and avoid hard acceleration until the signal circuit is checked. A false upstream reading can interfere with fuel control, raise fuel consumption and emissions, and potentially harm the catalyst if the mixture remains wrong.
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.