P2256
O2 Sensor Negative Current Control Circuit High Bank 2 Sensor 1
Fuel & air metering
Generic OBD-II
Medium
What it means
P2256 means the negative current control circuit for the bank 2, sensor 1 wide-band air/fuel sensor is reading too high. This circuit is part of how the ECM drives and reads the sensor's pump cell, so a fault makes the sensor's air/fuel signal unreliable and the ECM defaults to open-loop fueling. It usually traces to a wiring short, an open, or a failing sensor.
Medium
Can I keep driving? Drivable, but the ECM loses accurate air/fuel feedback from the primary bank 2 sensor, so fueling and economy can suffer until it's fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Rough running or slightly uneven idle
- Increased fuel consumption
- Hesitation as the ECM falls back to open-loop fueling
Common causes
Most likely first
- Faulty wide-band air/fuel (O2) sensor on bank 2, sensor 1Likely
- Negative current control wire shorted to voltage or open in the sensor circuitCommon
- Poor connection or corrosion at the sensor connectorCommon
- Chafed or damaged sensor harnessLess often
- Rarely, a faulty ECM/PCM current-control driverLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm it's the bank 2, sensor 1 circuit.
- Inspect the sensor connector and harness for shorts to voltage, opens, and corrosion.
- Backprobe the negative current control circuit to see whether it's pinned high connected vs. unplugged.
- Cross-check against the wiring diagram to isolate a harness fault from the sensor or ECM.
- If the wiring checks out but the sensor is faulty, replace the air/fuel sensor and retest.
FAQ
Quick answers
Is it safe to drive with P2256?+
Short term yes, but without accurate feedback from the main bank 2 air/fuel sensor the engine runs on default fueling, hurting economy and emissions.
Can I just clear P2256?+
It returns until the current-control circuit fault or sensor is repaired.
Related codes
Often seen with P2256
Read & clear P2256 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX