Code Definition

P0031 — Oxygen A/F Sensor Heater Control Circuit Low Bank 1 Sensor 1

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Toyota

About P0031

P0031 is a generic (obd-ii standard) powertrain diagnostic trouble code recorded for Toyota vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0031 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.

Because P0031 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The upstream Air Fuel Ratio (AFR) sensor on Bank 1 Sensor 1 is a heated wideband sensor that must reach approximately 650 to 750 degrees C before it can provide an accurate lambda reading to the Engine Control Module (ECM). Toyota supplies battery voltage to one side of the sensor heater through the EFI main relay and the ECM pulses the ground side on and off to control heater current. DTC P0031 sets when the ECM detects the heater control circuit voltage is lower than the expected threshold for the commanded duty cycle, typically indicating a short to ground, a heater element internally short...

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