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P0135 — O2 sensor heater circuit (Bank 1, Sensor 1)

The upstream oxygen sensor heater circuit is not working properly. Without heat, the sensor takes too long to reach operating temperature—especially in a cold winter.

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Likely causes

  • Failed upstream O2 sensor (burned heater element)
  • Blown O2 heater fuse or relay
  • Harness or connector damaged by heat or corrosion

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Recommended checks

  1. 1

    Test O2 heater resistance

  2. 2

    Check the heater circuit fuse and relay

  3. 3

    Replace the upstream O2 sensor if the heater is open

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Parts to replace