Code Definition

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

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

About P1166

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

The primary bank 1 air fuel ratio sensor contains an internal heater element that the Engine Control Module (ECM) energises to bring the sensor up to operating temperature quickly so it can measure the exhaust air fuel ratio accurately, especially soon after a cold start. The ECM monitors heater current and circuit condition. DTC P1166 sets when the ECM detects the heater current too low or too high, or an open or short in the heater circuit, during startup or normal operation. With the heater faulted the sensor warms slowly or not at all, delaying closed loop fuel control. The driver may noti...

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