Lambda Control

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

Lambda (λ) control regulates the air-fuel ratio (AFR) using oxygen sensor feedback. Maintaining precise AFR is essential for three-way catalyst efficiency, emissions compliance, and engine protection under high load.

Visión general

Lambda = 1.0 represents stoichiometric combustion (14.7:1 AFR for gasoline). The ECU uses wideband or narrowband O2 sensors to measure exhaust oxygen and adjust fuel injection accordingly.

Controlled Signals

  • Pre-catalyst lambda sensor
  • Post-catalyst lambda sensor
  • Fuel injection pulse width
  • Short-term fuel trim (STFT)
  • Long-term fuel trim (LTFT)

Maps Involved

  • Target Lambda Maps vs RPM/load
  • Closed-Loop Enable Maps
  • Enrichment Maps (WOT protection)
  • Fuel Trim Limits
  • Catalyst Heating Lambda Maps

Logic Sequence

Target Lambda Lookup → Injection Calculation
         ↓
Lambda Sensor Feedback
         ↓
PID Controller → STFT Adjustment
         ↓
LTFT Learning (if deviation persists)

Calibration Objectives

  • Maintain lambda = 1.0 during closed-loop operation
  • Enrich appropriately for WOT protection
  • Enable fast catalyst light-off

Calibration Strategy

  • Target lambda 0.80-0.85 at WOT for engine protection
  • Extend closed-loop range for better fuel economy
  • Verify fuel trims remain within ±10% after tuning

Diagnóstico

  • P0171/P0172 lean/rich codes
  • Catalyst efficiency codes (P0420/P0430)
  • Lambda sensor response faults

Best Practices

  • Always verify AFR with wideband during WOT tuning
  • Replace aging O2 sensors to maintain accuracy
  • Coordinate lambda targets with ignition timing

⚡

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