Code Definition

P1166 — Heated Oxygen Sensor 2 bank 2 voltage low

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Nissan

About P1166

P1166 is a manufacturer-specific powertrain diagnostic trouble code recorded for Nissan vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1166 is stored, the module has detected a signal or supply voltage lower than the expected operating range; a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1166 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

Heated oxygen sensor 2 is the rear, post catalyst oxygen sensor, and this code applies to the sensor on bank 2, downstream of the catalytic converter. It compares oxygen leaving the catalyst against outside air, generating roughly 1V rich to near 0V lean, and the ECM uses it mainly to monitor catalyst efficiency and make slow fuel corrections. DTC P1166 is set when the ECM sees the bank 2 rear sensor signal biased low, meaning it is reporting lean or its voltage is not reaching the expected level. This can be caused by an aged or contaminated rear sensor, an exhaust leak near the sensor, a gen...

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