Secondary Air System

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

Secondary Air Injection (SAI) pumps fresh air into the exhaust manifold during cold start. This provides oxygen for afterburning of unburned hydrocarbons and accelerates catalyst light-off, significantly reducing cold-start emissions.

Overview

The secondary air pump runs for 30-120 seconds after cold start. Fresh air enables exothermic reactions in the exhaust, rapidly heating the catalyst to operating temperature.

Controlled Signals

  • Secondary air pump relay
  • Secondary air valve
  • Coolant temperature
  • Lambda sensors

Maps Involved

  • SAI Enable Temperature Maps
  • SAI Duration Maps
  • SAI Monitoring Maps
  • Lambda Offset Maps (during SAI)

Logic Sequence

Cold Start Detected → Temperature Check
         ↓
Enable SAI Pump & Valve
         ↓
Monitor Lambda for Expected Response
         ↓
Disable After Timeout or Temp Reached

Calibration Objectives

  • Rapid catalyst light-off
  • Minimize cold-start HC/CO
  • Verify system function for OBD compliance

Calibration Strategy

  • SAI delete requires ECU modification to disable monitoring
  • Pump failure sets codes — cannot simply disconnect
  • Performance builds may delete SAI to simplify exhaust

Diagnostics

  • SAI flow insufficient
  • SAI pump inoperative
  • SAI valve stuck

Best Practices

  • SAI delete is emissions-related and illegal in many regions
  • Check valve prevents exhaust backflow — must function correctly

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