P0138 Fault Code

O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)

• What does that mean?
• Symptoms
• Causes
• Solutions

The P0138 fault code signifies a potential issue in the O2 Sensor circuit. Specifically, it indicates that there is high voltage detected from the O2 Sensor located on Bank 1, Sensor 2. This sensor is responsible for measuring the level of oxygen in the exhaust gases and helps to manage the air-fuel mixture for optimal combustion efficiency. High voltage readings can disrupt this function, potentially leading to poor vehicle performance and increased emissions.

What are the symptoms of the P0138 code?

Drivers may notice several symptoms when the P0138 code is present, including:

• Illuminated Check Engine Light.
• Poor fuel economy due to an incorrect air-fuel mixture.
• Rough idling or difficulty starting the vehicle.
• Increased emissions potentially leading to a failed emissions test.
• A noticeable decrease in engine performance or acceleration.

What causes the P0138 code?

Some common causes of the P0138 code include:

• A failing O2 sensor due to wear or age.
• A wiring issue, such as damaged or frayed wires connected to the O2 sensor.
• A malfunctioning Engine Control Module (ECM).
• Exhaust leaks near the sensor which can alter readings.
• Contaminants in the sensor, like oil or anti-freeze, affecting its performance.

How to fix P0138?

To resolve the P0138 fault code, consider the following steps:

• Inspect the wiring and connectors leading to the O2 sensor for damage or corrosion and repair as needed.
• Replace the faulty O2 sensor if it is confirmed to be malfunctioning.
• Check for and repair any exhaust leaks that may be affecting the sensor's readings.
• If problems persist after addressing the sensor and wiring, consider testing the Engine Control Module (ECM) for faults.