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P2256 — O2 Sensor Negative Current Control Circuit High Bank 2 Sensor 1

Manufacturer-specificPowertrain (engine & transmission)

P2256 indicates that the powertrain control module has detected a high voltage condition in the negative current control circuit for the upstream oxygen sensor on bank 2 (sensor 1). The sensor’s heater circuit is being commanded to draw more current than expected, suggesting a fault in the sensor, wiring, or related components.

Symptoms

What causes it — most likely first

1. Faulty Bank 2 Sensor 1 O2 sensor (heater element)

The heater circuit inside the upstream O2 sensor can develop an internal short, causing excessive current draw.

2. Damaged or corroded wiring/connector for the sensor’s heater circuit

Pinched, cracked, or corroded wires or connectors can create a low‑resistance path, leading to a high‑current condition.

3. Short to ground in the heater control circuit

A grounding fault in the circuit downstream of the PCM can cause the PCM to read a high voltage on the negative side.

4. Failed heater control driver (PCM output stage)

Although rare, the PCM’s driver transistor that switches the sensor heater can malfunction and output excessive voltage.

How it's diagnosed

  1. Inspect the bank 2 sensor 1 heater circuit wiring and connector for damage, corrosion, or loose pins.
  2. Measure resistance of the O2 sensor heater element (typically 2–4 Ω) and compare to specification.
  3. Perform a voltage test on the heater circuit with the ignition on; verify that voltage does not exceed the rated value.
  4. If wiring and sensor test normal, conduct a bench test or swap the sensor with a known good one to see if the code clears.
  5. If the code persists after confirming sensor and wiring are good, test the PCM heater control output with a known good sensor in place.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationManufacturer-specific (P1/B1/C1/U1)
Related codesP2250 — O2 Sensor Reference Voltage Circuit HiP2251 — O2 Sensor Negative Current Control CirP2252 — O2 Sensor Negative Current Control CirP2253 — O2 Sensor Negative Current Control CirP2254 — O2 Sensor Negative Current Control CirP2255 — O2 Sensor Negative Current Control Cir

Frequently asked

Can a bad PCM cause P2256?

It is possible but uncommon. The PCM’s heater‑control driver can fail, but most cases are traced to the sensor or its wiring before replacing the PCM.

Do I need to replace the O2 sensor immediately?

If the sensor’s heater resistance is out of spec or visual inspection shows damage, replacement is recommended. Otherwise, verify wiring and connectors first.

Will clearing the code without fixing anything work?

The code will likely return after a drive cycle because the underlying fault (high heater current) remains.

Why do some sources suggest replacing the PCM for this code?

Those recommendations are often based on misinterpretation of the code. In real‑world experience, the PCM is rarely the cause; focus on the sensor, wiring, and ground issues first.