P0138
PowertrainOxygen Sensormoderate severityO2 Sensor Circuit High Voltage Bank 1 Sensor 2
What P0138 Means
The downstream O2 sensor on Bank 1 is reading high voltage consistently.
Symptoms
- Check Engine Light
- Failed emissions
- May indicate catalyst failure
Common Causes
- Faulty sensor
- Catalytic converter failure
- Rich running condition
Diagnostic Steps
- Test sensor voltage
- Check catalyst efficiency
- Monitor upstream vs downstream O2 patterns
Where to start: Replace sensor. If catalyst failed, replace catalytic converter.
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