P0031low severityPowertrain
HO2S Heater Control Circuit Low Bank 1 Sensor 1
on 2003 Subaru Legacy 3.0L H6 · AWD
What this code means
The voltage in the Bank 1 Sensor 1 O2 heater circuit is lower than expected.
Symptoms
- Check Engine Light
- Extended warmup time
- Poor cold-start emissions
Common causes
- Short to ground in heater circuit
- Faulty O2 sensor
- Corroded connector
Diagnostic steps
- Test heater circuit voltage
- Check for shorts to ground
- Test sensor heater resistance
- Inspect connector
Repair notes
Repair short or replace O2 sensor.
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