Code Definition

P103D — A/F Sensor Heater Circuit Performance Bank 2 Sensor 1 Stuck ON

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

About P103D

P103D is a manufacturer-specific 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 P103D is stored, the module has detected a plausibility fault — the measured value is in the electrical range but is not consistent with expected operating behaviour; 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.

P103D 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 P103D is set when the Engine Control Module (ECM) detects that the air fuel (A/F) sensor heater circuit for Bank 2, Sensor 1 remains continuously active or draws more current than expected when it should be off. The heater rapidly warms the sensor element so the ECM can use the signal for accurate air fuel ratio control soon after start up. Bank 2 is the cylinder bank that does not contain cylinder number 1, and Sensor 1 is the upstream sensor mounted before the catalytic converter. When the heater circuit stays on or overdraws current, the ECM stores the code and illuminates the malfuncti...

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