P0138: Downstream O2 sensor circuit high voltage (Bank 1 Sensor 2)
You can keep driving. Get it checked when convenient.
Can I drive with P0138?
Yes, you can keep driving. Post-catalyst sensor reporting high voltage; vehicle runs normally without engine risk.
What does P0138 mean?
P0138 stands for O2 Sensor Circuit High Voltage (Bank 1, Sensor 2).
Symptoms you may notice
- Check engine light on with no noticeable change in how the car drives
- Vehicle fails state emissions smog test
- Normal engine power and shifting
How much does it cost to fix?
Repair costs for code P0138 depend on the specific underlying root cause, ranging from simple DIY checks to component replacement. The table below lists the most common causes and rough price ranges in USD:
- Internal short in the downstream sensor
- Heater circuit wire shorted to signal wire
- Corroded connector pins bridging current
- Severely rich fuel mixture reaching catalyst
What to do next
- Inspect the downstream sensor pigtail harness for melting or physical pinching.
- Unplug the sensor and test if scanner voltage drops to 0V.
- Replace the downstream Bank 1 Sensor 2 oxygen sensor.
Last updated: October 2026
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General guidance only, not a professional diagnosis. If the check-engine light is flashing, or the car is running rough, overheating or losing power, stop driving and get help.
About this code
Code P0138 occurs when Bank 1 Sensor 2 voltage exceeds 1.2 volts. Often, 12-volt battery power from the internal heater circuit shorts into the 1-volt signal wire inside a melted harness. Replacing the sensor and tucking the harness safely away from hot exhaust parts fixes the problem.