Posts Tagged: P0138 code

Common Causes of a P0138 Code: O2 Sensor High Voltage

P0138 Code: Causes, Symptoms, and Fixes Explained Quick Summary When I diagnose a P0138 code, I know the engine computer is detecting a high-voltage signal from the rear oxygen sensor (Bank 1, Sensor 2). That usually means the sensor is reporting a consistently rich condition—or the circuit itself is faulty. In most cases, the root cause is a • failing O2 sensor • wiring issue • exhaust leak, • or a true rich-running condition. The fix comes down to verifying sensor data, checking wiring integrity, and confirming whether the engine … Read More