OBD-II FAULT CODE
P0418

Secondary Air Injection System Relay "A" Circuit Malfunction

Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P0418.

PowertrainSystem
Electrical circuit / sensorCategory
MediumSeverity
  • Check Engine light
  • Poor drivability or reduced fuel economy depending on fault
  • Faulty related sensor/actuator
  • Wiring or connector issue
  • Poor ground/power supply
  • Control module fault is possible but less common
  • Scan all modules and record freeze-frame data before clearing codes
  • Check battery voltage and related fuses
  • Repair wiring/connector/fuse issues first
  • Replace the related sensor/actuator only after testing confirms failure
  • Use OEM service manual for brand-specific procedures
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Disclaimer: Information is provided for general guidance only and may not apply to all vehicles. Always consult a qualified technician.