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2020 MAZDA MAZDA3
2.5L Skyactiv-G I4 (186 hp)•AWD•AUTOMATIC•gas
2 active safety recalls on this vehicle — view recalls
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Repairs0Labor987Torque6478Fluid16DTC2264Battery2Maintenance0Recalls2
P1131moderate severityPowertrain

HO2S Bank 1 Sensor 1 Air/Fuel Ratio Too Lean

on 2020 Mazda Mazda3 2.5L Skyactiv-G I4 (186 hp) · AWD

What this code means

The upstream heated oxygen sensor on Bank 1 indicates a persistent lean air-fuel ratio. The PCM has been unable to correct the lean condition through fuel trim adjustments.

Symptoms

  • Check Engine Light
  • Rough idle
  • Hesitation
  • Poor acceleration
  • Possible misfires

Common causes

  • Vacuum leak in intake system
  • Low fuel pressure
  • Dirty or faulty MAF sensor
  • Faulty O2 sensor reading lean incorrectly
  • Exhaust leak before sensor

Diagnostic steps

  1. Check for vacuum leaks with smoke test
  2. Monitor fuel trim values on scan tool
  3. Check fuel pressure at idle and under load
  4. Clean MAF sensor
  5. Inspect for exhaust leaks near O2 sensor

Repair notes

Repair vacuum leaks; check fuel pressure and MAF sensor; replace the O2 sensor if faulty.

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