FixItFor.Us
P codepowertrainMedium severity

P2233O2 Sensor Signal Circuit Shorted to Heater Circuit (Bank 1 Sensor 3)

The signal wire of the third oxygen sensor on Bank 1 is shorted to its heater circuit, so the PCM sees heater voltage instead of a valid exhaust reading.

Definition

On vehicles equipped with a third Bank 1 oxygen sensor (typically behind a second catalytic converter), the PCM expects the Sensor 3 signal to remain in the normal 0-1 volt range. When the signal is pulled toward battery voltage or oscillates with the heater's duty cycle, the PCM sets P2233 for a signal-to-heater short. Driveability is usually unaffected, but the MIL turns on, the catalyst monitor for that converter cannot run, and the vehicle will not pass an OBD emissions test.

Common causes

  • Internal sensor failure shorting the heater element to the signal element
  • Harness chafing that lets the heater power wire contact the signal wire
  • Moisture or contamination inside the sensor connector bridging terminals
  • Heat-damaged pigtail insulation near the exhaust
  • Improperly spliced universal replacement sensor

Common misdiagnoses

  • Rear catalytic converter replaced for a suspected efficiency failure
  • Wrong oxygen sensor replaced (Sensor 1 or 2 instead of Sensor 3)
  • PCM condemned when the fault is a wiring or sensor short
  • Exhaust repairs made chasing a nonexistent leak

Troubleshooting steps

  1. 1.Identify the correct sensor location

    Sensor 3 on Bank 1 is the furthest downstream sensor on that bank, after the second converter; confirm with the vehicle's sensor layout before testing anything.

  2. 2.Watch the B1S3 voltage PID on a scan tool

    A reading stuck well above 1.0 V or snapping toward system voltage indicates heater feed voltage on the signal circuit.

  3. 3.Unplug the sensor and check the harness side

    With the sensor disconnected and key on, the signal circuit should show only bias voltage (about 0.45 V); persistent battery voltage means a harness short.

  4. 4.Check for continuity between heater and signal pins at the sensor

    Any measurable resistance between heater pins and signal pins (should be open) confirms an internal sensor short — replace the sensor.

  5. 5.Inspect and repair wiring, then verify the fix

    Repair chafed sections with heat-resistant loom, clear the code, and confirm the signal returns to a normal slow-switching 0-1 V pattern.

Related codes