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DTC codes / P00xx · Fuel and air metering and auxiliary emission controls / P0055

P0055HO2S Heater Resistance (Bank 1 Sensor 3)

P0055 indicates that the powertrain control module has detected an abnormal electrical resistance in the heater circuit of the downstream oxygen sensor on bank 1, which is sensor 3. The computer monitors the heater current and compares it to expected values; when the resistance falls outside the acceptable range, it sets this code and illuminates the check engine light.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • A slight decrease in fuel economy because the sensor takes longer to reach operating temperature
  • Possible rough idle or hesitation during cold starts if the sensor remains cold longer than normal
  • In some vehicles, the engine may enter a default mode that slightly reduces performance
  • No drivability issues in most cases, as the heater only affects sensor readiness
  • Occasionally, a failed heater can cause a blown fuse that also disables other circuits

Common causes, most likely first

  1. Failed oxygen sensor heater element inside the sensor
  2. Open or shorted wiring in the heater circuit between the sensor and the control module
  3. Corroded or loose electrical connector at the oxygen sensor
  4. Blown fuse or faulty relay that supplies power to the heater circuit
  5. Internal fault in the powertrain control module driver for the heater circuit
  6. High resistance in the ground circuit for the oxygen sensor heater

How to diagnose and fix it

  1. Inspect the oxygen sensor connector for corrosion, moisture, or loose pins and clean or repair as needed
  2. Check the heater circuit fuse and relay, replacing any that are blown or faulty
  3. Measure the resistance of the heater element with a multimeter and compare to the manufacturer's specification
  4. Test for voltage and ground at the sensor connector with the key on to verify power and ground are present
  5. Check continuity and resistance of the wiring between the sensor and the control module to rule out open or shorted wires
  6. If the heater resistance is out of specification, replace the oxygen sensor with a quality direct-fit unit
  7. Clear the code and perform a road test to verify the repair and ensure the monitor completes

Why the heater circuit fails more often than the sensor

  • The heater element inside the oxygen sensor is a common failure point, but a corroded connector or chafed wire often mimics a failed sensor and is missed during diagnosis.
  • A blown fuse for the oxygen sensor heater can be caused by a shorted sensor or wiring, so replacing the fuse without finding the root cause will lead to a repeat failure.
  • Some vehicles use a shared power supply for multiple oxygen sensor heaters, so a fault in one circuit can affect others and set additional codes.
  • The code does not always mean the sensor is completely dead; the heater may still function but have resistance slightly out of range, causing intermittent symptoms.
  • On vehicles with a wideband sensor, the heater circuit is critical for accurate air-fuel ratio measurement, and a fault can cause drivability issues beyond a simple check engine light.

Can I keep driving with P0055?

You can generally continue driving with this code because the heater circuit only affects how quickly the sensor reaches operating temperature, but avoid extended idling and schedule a diagnosis soon to prevent potential fuel economy loss or secondary issues.

Tools that help

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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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