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

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.

Bank 2 is the side without cylinder 1, so it only exists on V or boxer engines. Sensor 1 is the oxygen sensor before the catalytic converter.

Symptoms

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

Most likely causes

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

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the wiring and connector of the sensor indicated
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Look for exhaust leaks
4. Check the signal in live data with the engine warm
5. Check the fuse and the heater resistance if the code mentions it
6. Replace the sensor if it has power and does not respond

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P2256 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 2: Fuel injection
• 56: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2256?

Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.

What causes code P2256?

The most common causes are: reference ground wire shorted to heater supply or battery voltage; internal short in the wide-band sensor; fault in the sensor interface of the ECM.

Related codes

• P2253O2 Sensor Negative Current Control Circuit High (Bank 1 Sensor 1)
• P2254O2 Sensor Negative Current Control Circuit/Open (Bank 2 Sensor 1)
• P2255O2 Sensor Negative Current Control Circuit Low (Bank 2 Sensor 1)
• P0152O2 Sensor Circuit High Voltage Bank 2 Sensor 1

Sources

• law.cornell.edu: 13 CCR 1968.2
• newtonnet.co.uk: fordobd2012
• fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.