P0138 – O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
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Symptoms
- Rough idle
- Hesitation
- Poor acceleration
- High fuel trims
- Check engine light
Causes
- Rich fuel mixture
- Faulty O2 sensor
- Exhaust leak
- Wiring issue
- Contaminated sensor
Diagnosis
- Inspect O2 wiring
- Check fuel trims
- Inspect exhaust leaks
- Scan live data
- Test sensor response
Repair
- Replace O2 sensor
- Fix exhaust leaks
- Repair wiring
- Check fuel trims
- Address rich mixture