P0139 Fault Code

O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)

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

The P0139 code indicates that the Oxygen (O2) sensor circuit for Bank 1 Sensor 2 is experiencing a slow response. This sensor is responsible for measuring the amount of oxygen in the exhaust gases after they pass through the catalytic converter. A slow response from this sensor suggests that it may be faulty or that there are issues with the exhaust system or wiring.

What are the symptoms of the P0139 code?

Common symptoms associated with a P0139 code include:

• Illuminated Check Engine Light (CEL).
• Reduced fuel efficiency due to incorrect air-fuel mixture.
• Poor engine performance, such as rough idling or hesitations during acceleration.
• Emission failures during testing due to improper readings from the O2 sensor.

What causes the P0139 code?

Several factors can contribute to a slow response from Bank 1 Sensor 2, including:

• A failing or malfunctioning O2 sensor.
• Exhaust leaks near the sensor, which can affect readings.
• Wiring or connector issues such as corrosion, shorts, or open circuits.
• Contaminated or degraded sensor from exposure to harmful substances.
• Engine performance issues, such as misfire or poor combustion, affecting exhaust composition.

How to fix P0139?

To resolve a P0139 code, follow these steps:

• Use an OBD-II scanner to confirm the code and check for other related codes.
• Inspect the wiring and connectors for the O2 sensor for signs of damage or corrosion.
• Check for exhaust leaks near the sensor; repair any leaks found.
• Test the O2 sensor using a multimeter to ensure it is functioning within specifications; replace it if it is faulty.
• Clear the trouble codes and take the vehicle for a test drive to see if the code returns.