P2256: O2 Sensor Negative Current Control Circuit High (Bank 2 Sensor 1)

What does P2256 mean?

P2256 means the negative current control line (reference ground) of the bank 2 upstream wide-band sensor reads too high, typically a short to battery or heater voltage. No manufacturer publicly documents P2256 with thresholds. Ford's OBD summaries send a short to battery on any wide-band sensor line to P0152 and reserve P2254 for the open line; VW's 2014 books also list only P2254 for this circuit. CARB requires fuel-control sensors to be checked for circuit continuity and out-of-range values, with separate codes where feasible. P2253 is the bank 1 counterpart, P2255 the low-side fault, P2254 the open circuit. A short to voltage can damage the sensor or the interface, so the wiring should be checked before a new sensor is fitted.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light
• Higher fuel consumption
• Repeat failure of a new sensor if the wiring short remains

Common causes

• High Reference ground wire shorted to heater supply or battery voltage
• Medium Internal short in the wide-band sensor
• Low Fault in the sensor interface of the ECM

Likelihood is a general estimate across vehicles; your make and model may differ.