OBD-II code guide
P0138 Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 means the downstream oxygen sensor voltage on bank 1 is higher than expected.
What it means
The post-catalyst sensor may show a rich signal, wiring short, or sensor fault.
Common symptoms
- Check engine light
- Poor fuel economy in some cases
- Emissions failure
- Usually mild symptoms
- Possible rich running signs
Likely causes
- Downstream oxygen sensor fault
- Signal wire short
- Rich running condition
- Connector contamination
- Exhaust or catalyst issue
First checks
- Check for rich codes.
- Inspect downstream wiring.
- Review fuel trims.
- Do not replace the catalytic converter before checking sensor data.