P0055 indicates that the powertrain control module (PCM) has detected a heater circuit malfunction in the oxygen sensor for Bank 1, Sensor 3 (the downstream sensor). This code is set when the sensor's heater resistance is outside the expected range, often due to a failed sensor or wiring issue.
The heater element inside the sensor has failed or its resistance is out of specification. This is the most common cause.
Wiring to the sensor heater circuit may be broken, shorted, or corroded, especially near the exhaust or connector.
A blown fuse in the oxygen sensor heater circuit will prevent power from reaching the sensor.
A defective relay or open circuit in the power supply to the heater can cause the code.
Rarely, the PCM may have an internal fault affecting the heater control circuit. This is the least likely cause and should only be considered after all other possibilities are ruled out.
Yes, in most cases the vehicle will remain drivable. However, the check engine light will be on, and the oxygen sensor heater malfunction may cause the catalyst monitor to run incompletely, potentially leading to an emissions test failure. It is best to address the issue promptly.
It can. A faulty downstream oxygen sensor heater may cause the PCM to run in a default mode, which can slightly increase fuel consumption. However, the impact is usually minor compared to a failed upstream sensor.
Almost never. The PCM is rarely the cause of this code. The vast majority of cases are due to a failed oxygen sensor, wiring issues, or a blown fuse. Only consider PCM replacement after thoroughly testing the sensor and circuits.
P0036 indicates a heater circuit malfunction (open or short) for the same sensor, while P0055 specifically indicates the heater resistance is out of range. Both point to the same sensor and similar causes, but the diagnostic approach may differ slightly.