Code Definition

P101D — A/F Sensor Heater Circuit Performance Bank 1 Sensor 1 Stuck ON

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

About P101D

P101D 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 P101D 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.

P101D 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 P101D is a Toyota rationality fault set when the Engine Control Module (ECM) detects that the Bank 1 Sensor 1 Air Fuel Ratio (AFR) sensor heater circuit continues to draw current or remains grounded through the ECM low side driver after the heater has been commanded off. The AFR sensor heater is normally pulse width modulated to hold the sensor element at approximately 750 degrees C, and the ECM monitors the control line to verify it switches cleanly between ground and open. This code typically indicates a short to ground on the heater control wire, a failed ECM internal driver transistor ...

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