Oxygen Sensors (Lambda)

🧠 Part of the TuningBot ECU Knowledge Base — in-depth documentation on ECU logic, maps, emissions systems and safe calibration methods.

Oxygen sensors (lambda sensors) measure the oxygen content of exhaust gas. The ECU uses this information for closed-loop fuel control and catalyst efficiency monitoring. They are essential for emissions compliance and fuel management.

Vue d'ensemble

Pre-catalyst sensors provide AFR feedback for fuel control. Post-catalyst sensors monitor catalyst efficiency by comparing oxygen storage capability to expected values.

Sensor Types

  • Narrowband — switches at stoichiometric (lambda = 1)
  • Wideband — linear output across AFR range
  • Planar — fast response, integrated heater
  • NOx sensors — measure NOx and O2 (diesel)

ECU Usage

  • Closed-loop fuel control
  • Fuel trim adaptation (STFT/LTFT)
  • Catalyst efficiency monitoring
  • WOT enrichment verification

Calibration Considerations

  • Rear O2 simulation needed if catalyst removed
  • Wideband sensors required for accurate WOT tuning
  • Sensor age affects response time and accuracy

Diagnostics

  • O2 sensor circuit faults
  • Response time faults
  • Heater circuit faults
  • Catalyst efficiency codes (P0420/P0430)

Best Practices

  • Replace O2 sensors at recommended intervals
  • Use quality sensors matching OE specifications
  • Protect sensors from silicone contamination

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