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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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Repairs0Labor984Torque6456Fluid16DTC3770Battery2Maintenance0Recalls2
P1132moderate severityPowertrain

HO2S Bank 1 Sensor 1 Air/Fuel Ratio Too Rich

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 rich air-fuel ratio. The PCM fuel trim correction has reached its maximum lean limit but cannot correct the rich condition.

Symptoms

  • Check Engine Light
  • Rich exhaust smell
  • Black exhaust smoke
  • Poor fuel economy
  • Fouled spark plugs

Common causes

  • Leaking fuel injector
  • High fuel pressure from faulty regulator
  • Faulty O2 sensor reading rich incorrectly
  • EVAP purge valve stuck open
  • Coolant entering combustion chamber

Diagnostic steps

  1. Monitor fuel trim values on scan tool
  2. Check fuel pressure with gauge
  3. Inspect spark plugs for rich fouling
  4. Test for leaking injectors
  5. Check EVAP purge valve operation

Repair notes

Correct the source of the rich condition; check fuel pressure, injectors, and the O2 sensor.

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