P0055 HO2S Heater Resistance Bank 1 Sensor 3

On bank 1, this monitor checks the heating element of sensor 3 further downstream not for an open or short circuit, but for its resistance. Many systems measure it once after a genuine cold start, when coolant and intake air temperatures show that the sensor is at ambient temperature, and correct the value for temperature; some manufacturers evaluate the heater current instead. The code is set when the value lies outside the limits for this sensor type, typically because the element has aged. Since the test often runs only after a long standstill, the code may take a night to confirm or clear.

Likely causes

Symptoms

• Check engine light on, sometimes only after a cold start
• Readiness for the sensor heater stays incomplete
• Usually no drivability symptoms

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, newtonnet.co.uk, static.nhtsa.gov.