A failed or contaminated rear oxygen sensor. A short to voltage in the wiring. A real rich condition.

P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)

Q: What does P0138 mean?

P0138 means bank 1's rear oxygen sensor is stuck at high voltage, from a failed sensor, wiring or a rich condition. The rear oxygen sensor on bank 1 is staying at high voltage. It may be failed or contaminated, its wiring shorted to voltage, or the engine running rich.

Oxygen sensors

P0138 means bank 1's rear oxygen sensor is stuck at high voltage, from a failed sensor, wiring or a rich condition.

The rear oxygen sensor on bank 1 is staying at high voltage. It may be failed or contaminated, its wiring shorted to voltage, or the engine running rich.

Can I keep driving? Yes, for now.

Safe to drive for now, but fix any rich condition soon to protect the converter.

Common causes

A failed or contaminated rear oxygen sensor
A short to voltage in the wiring
A real rich condition

Symptoms

Check-engine light
Sometimes poor fuel economy

Common on: Toyota Tacoma

What to check first

Check for rich codes (P0172, P0175) first.
Inspect the wiring for damage.
Watch the sensor with a scan tool.
Replace the sensor if it stays high with a normal mixture.

What does P0138 mean on your vehicle?

The likely cause depends on your engine. iRepair researches your exact year, make, model and engine (service bulletins, recalls and owner reports) and tells you what to check first. Your first 3 questions are free.

Ask iRepair about P0138

No scanner? Most auto parts stores read check-engine codes for free.

Related codes

General guidance for P0138 on most vehicles. Some makers use the same code a little differently; confirm in the service information for your vehicle, put safety first, and see a professional when in doubt.