P0138 O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)
What does P0138 mean?
P0138 — O2 Sensor Circuit High Voltage (Bank 1, Sensor 2) (bank 1). This is an OBD-II diagnostic trouble code a scanner retrieves when your vehicle's computer detects o2 sensor circuit high voltage (bank 1, sensor 2) on bank 1. The level of risk depends on how the vehicle is currently running and how long you've been driving with the light on.
Common causes of P0138
- Failed downstream oxygen sensor
- Shorted signal wire to voltage
- Rich mixture overwhelming the catalyst
- Damaged sensor
How to fix P0138
- Watch downstream voltage at steady state vs acceleration
- Check short-to-voltage on the signal wire
- Review fuel trims for a rich condition
- Replace the sensor if stuck high
- Re-check catalyst monitor behavior after repair