P1131moderate severityPowertrain
HO2S Bank 1 Sensor 1 Air/Fuel Ratio Too Lean
on 2005 Mazda Mazda3 2.0L I4 · FWD
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
- Check for vacuum leaks with smoke test
- Monitor fuel trim values on scan tool
- Check fuel pressure at idle and under load
- Clean MAF sensor
- Inspect for exhaust leaks near O2 sensor
Repair notes
Repair vacuum leaks; check fuel pressure and MAF sensor; replace the O2 sensor if faulty.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1