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

The Technical Definition: This code points to a high voltage reading on the oxygen sensor circuit for bank 1, sensor 2.

Common Symptoms: The check engine light will illuminate, and there could be a slight decrease in overall fuel efficiency.

Typical Fix: Inspect the wiring harness for the downstream oxygen sensor for any visible shorts, melting, or damage. If the wiring is completely intact, replacing the oxygen sensor itself is usually the solution.