DTC codes / P00xx · Fuel and air metering and auxiliary emission controls / P0054
P0054 means the engine computer has detected an out-of-range resistance in the heater circuit of the downstream oxygen sensor on bank 1, which is the sensor after the catalytic converter. The heater is a small element inside the sensor that brings it up to operating temperature quickly so the computer can monitor catalyst efficiency, and the code sets when the measured current or voltage does not match the expected value for the sensor's temperature.
Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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