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P codepowertrainMedium severity

P2276O2 Sensor Signal Biased/Stuck Lean Bank 2 Sensor 3

The third oxygen sensor on Bank 2 is stuck reporting a lean exhaust condition and does not respond when the mixture goes rich.

Definition

On vehicles with a third Bank 2 oxygen sensor (downstream of a second catalytic converter), the PCM checks that the Sensor 3 signal can move through its full range during commanded rich excursions. When the voltage remains pinned low near 0.1 V and never rises during these tests, the PCM sets P2276 for a signal biased or stuck lean. The engine typically drives normally, but the MIL comes on, monitoring of the rear converter is disabled, and the vehicle will fail an OBD emissions test.

Common causes

  • Worn-out or contaminated oxygen sensor unable to generate signal voltage
  • Exhaust leak upstream of the sensor admitting outside air
  • Open or grounded signal wire, or corroded connector terminals
  • Poor sensor ground through the exhaust or harness
  • Actual persistent lean exhaust condition on Bank 2

Common misdiagnoses

  • Rear catalytic converter replaced when the sensor or an exhaust leak is the cause
  • Sensor 1 or Sensor 2 on Bank 2 replaced instead of Sensor 3
  • Fuel system repairs made for what is only a dead sensor
  • Exhaust system replaced wholesale without pinpointing the leak

Troubleshooting steps

  1. 1.Locate the correct sensor

    B2S3 is the last sensor in the Bank 2 exhaust path; confirm sensor positions from the service information before condemning parts.

  2. 2.Inspect for exhaust leaks near the sensor

    Check flange gaskets, welds, and the sensor bung for soot or whistling at idle; even a small leak dilutes the exhaust sample and holds the reading lean.

  3. 3.Test sensor response with a forced rich condition

    While watching the B2S3 PID, create a brief rich event (throttle snap or propane enrichment); a healthy sensor should rise above 0.7 V within seconds.

  4. 4.Check the signal circuit and ground

    Verify bias voltage on the harness signal wire with the sensor unplugged and confirm less than 0.1 V drop across the sensor ground path with the engine running.

  5. 5.Replace the sensor if it fails to respond, then verify

    Fit an OE-quality sensor, clear the code, and drive the monitor conditions to confirm the fault does not return.

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