P0138 Code: O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
🟢 Low severity · drivable
Safe to drive — this downstream sensor fault mainly affects emissions monitoring.
What P0138 means
The bank 1 downstream oxygen sensor is reporting very high voltage. This is the sensor after the catalytic converter, so it's primarily an emissions concern.
Symptoms
- Check engine light is on
- Usually no driving symptoms
Common causes
- most common: Faulty downstream oxygen sensor
- common: Wiring shorted to power
- less common: Genuine rich running
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Replace the bank 1 downstream oxygen sensor | Yes | $60–200 |
| Repair shorted sensor wiring | Mechanic | $50–150 |
Frequently asked questions
Can I drive with a P0138 code?
Yes. It mainly affects emissions monitoring, not drivability.
What is the most common cause of P0138?
A faulty downstream oxygen sensor.
How much does it cost to fix a P0138?
Typically $60–$200 for a new downstream oxygen sensor.
Related codes
P0136
P0136 Code: O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)
P0137P0137 Code: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)
P0132P0132 Code: O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.