P0030low severityPowertrain
HO2S Heater Control Circuit Bank 1 Sensor 1
on 2016 Mazda Mazda3 2.5L I4 · FWD
What this code means
The PCM detected a malfunction in the heater circuit of the upstream heated oxygen sensor (Bank 1, Sensor 1).
Symptoms
- Check Engine Light
- Poor fuel economy
- Longer warmup emissions
- Failed emissions test
Common causes
- Faulty O2 sensor heater
- Blown fuse
- Wiring issue
- PCM heater driver failure
Diagnostic steps
- Check O2 sensor heater fuse
- Test heater circuit resistance (should be 2-30 ohms)
- Inspect wiring to sensor
- Check PCM heater control output
Repair notes
Replace O2 sensor if heater resistance is out of spec. Check fuse and wiring first.
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