P0138 Code: O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)
CodePage.genericDisclaimer
Qu'est-ce que cela signifie ?
Code P0138 indicates the downstream O2 sensor on Bank 1 is reading persistently high voltage.
Diagnostic system: Sensor circuit and live data
On a Subaru Outback, the P0138 code should be diagnosed as part of the sensor circuit and live data group. Related codes and live data from this same system can change the repair priority, so avoid replacing parts from the code name alone.
Most Common Causes for Subaru Outback
- Sonde lambda (O2) défectueuse
- Injecteur de carburant obstrué ou défectueux
- Faisceau de câblage endommagé ou cassé
Symptômes à surveiller
- Le voyant moteur est allumé
- Consommation de carburant accrue
- Échec au contrôle des émissions
CodePage.beforeReplacing
- Inspect the connector for corrosion, broken locks, oil intrusion, or heat damage.
- Verify 5V reference, ground, and signal with a multimeter where applicable.
- Compare live sensor data to realistic engine temperature, pressure, airflow, or throttle values.
- Check for blown fuses, weak battery voltage, and damaged connectors before buying major parts.
Comment Diagnostiquer
CodePage.commonMistakes
Replacing the named sensor without testing power, ground, signal, and wiring continuity first. Always confirm the fault with freeze-frame data, live data, visual inspection, and circuit checks before spending money on parts.
CodePage.faq
Can I drive with the P0138 code?
If the check engine light is solid, you can usually drive to a safe location or mechanic. If the light is flashing, pull over immediately to prevent catastrophic engine or catalytic converter damage.
Will the P0138 code clear itself?
Once the underlying problem is fixed, the engine computer will run its self-checks. If it passes over several drive cycles, the light will turn off automatically. You can also clear it immediately using an OBD2 scanner.
Will this code fail an emissions test?
Yes. If the Check Engine Light is on due to the P0138 code, your Subaru will automatically fail an OBD2 plug-in emissions or smog test.
What should I check first for P0138?
Inspect the connector for corrosion, broken locks, oil intrusion, or heat damage. Verify 5V reference, ground, and signal with a multimeter where applicable. Compare live sensor data to realistic engine temperature, pressure, airflow, or throttle values.
Join the Discussion
Estimation de réparation
Fuse, connector, wiring, cleaning, or basic inspection
Major component replacement after live data and circuit tests confirm failure
Comprend les pièces et la main-d'œuvre. Peut varier selon l'emplacement.
Sensor replacement can be moderate cost, but wiring and connector repairs are common and cheaper.
Difficulté de réparation (DIY)
Can usually be performed at home with basic hand tools.