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P codepowertrainMedium severity

P2236O2 Sensor Signal Circuit Shorted to Heater Circuit (Bank 2 Sensor 3)

The signal wire of the third oxygen sensor on Bank 2 is shorted to its heater circuit, corrupting the voltage signal sent to the PCM.

Definition

The PCM monitors the Bank 2 Sensor 3 oxygen sensor — the furthest downstream sensor on the bank opposite cylinder 1, found on vehicles with a second converter in that exhaust path — expecting a signal within 0-1 volt. When the signal rides up toward battery voltage or tracks the heater's switching pattern, the PCM sets P2236 for a signal-circuit-to-heater-circuit short. The engine typically runs normally, but the MIL illuminates, catalyst monitoring for that converter is disabled, and the vehicle will fail an OBD emissions inspection.

Common causes

  • Internal sensor failure shorting the heater element to the sensing element
  • Chafed or heat-damaged harness shorting the heater feed to the signal wire
  • Corroded or water-contaminated sensor connector bridging terminals
  • Pigtail insulation melted against exhaust components
  • Incorrectly wired universal replacement sensor

Common misdiagnoses

  • Bank 2 rear catalytic converter replaced unnecessarily
  • A different oxygen sensor on Bank 2 replaced instead of Sensor 3
  • PCM replaced for what is a simple wiring short
  • Fuel-system diagnosis pursued for a purely electrical signal fault

Troubleshooting steps

  1. 1.Confirm which sensor is B2S3

    Bank 2 is the cylinder bank not containing cylinder 1; Sensor 3 is the last sensor in that bank's exhaust stream — verify with the service manual before testing.

  2. 2.Monitor the B2S3 signal PID

    A voltage pinned above 1.0 V or jumping toward 12 V with the heater active confirms heater voltage is leaking onto the signal circuit.

  3. 3.Isolate sensor versus harness

    Unplug the sensor; if the harness-side signal circuit drops back to bias voltage (about 0.45 V), the sensor is internally shorted — if not, trace the harness.

  4. 4.Ohm-test heater-to-signal isolation at the sensor

    Resistance between heater pins and signal pins should read open; continuity confirms the sensor failed internally.

  5. 5.Repair or replace and verify monitors complete

    After repair, clear codes and drive the catalyst-monitor conditions to confirm the code does not reset and the monitor reaches ready status.

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