Code Definition

P1166 — Heated Oxygen Sensor 1, bank 1 - at control limit

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

About P1166

P1166 is a manufacturer-specific powertrain diagnostic trouble code recorded for Hyundai 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 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

During closed loop operation the Engine Control Module uses the upstream heated oxygen sensor on Bank 1 Sensor 1 to keep the air fuel mixture oscillating around the stoichiometric point, continuously adjusting injection within a defined control range. DTC P1166 is set on Hyundai and Kia vehicles when this oxygen sensor control reaches its control limit, meaning the ECM has applied the maximum correction the lambda loop allows yet still cannot hold the mixture at target. It indicates either a genuine mixture fault that exceeds the controller authority, such as a large air or fuel imbalance, or ...

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