Code Definition

P1166 — Primary Heated Oxygen Sensor (#1) heater circuit

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

About P1166

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

DTC P1166 is a Honda specific code for a fault in the primary, or upstream, Heated Oxygen Sensor (Sensor 1) heater circuit. The sensor contains an internal heating element that the Powertrain Control Module (PCM) energises to bring the sensor quickly to operating temperature so closed loop fuel control can begin. The PCM monitors the heater circuit and sets P1166 when it sees an open, a short, or a current draw outside the expected range. With this code set the sensor warms up slowly or not at all, which delays closed loop operation and can raise emissions, increase cold running fuel use, and ...

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