DTC P0139: Oxygen Sensor Slow Response (Bank 1, Sensor 2)

In the world of automotive diagnostics, diagnostic trouble codes (DTCs) act as guides, leading mechanics towards potential issues within a vehicle’s systems. Among these, DTC P0139 takes center stage as a significant indicator of problems related to the slow response of the oxygen sensor in Bank 1, Sensor 2. This comprehensive article delves into the causes, symptoms, inspection procedures, and effective solutions for addressing and resolving DTC P0139.

1. Causes of DTC P0139:

DTC P0139 emerges when the Engine Control Module (ECM) detects a slow response from the oxygen sensor located in Bank 1, Sensor 2. The underlying causes can encompass:

– Faulty oxygen sensor: An aging or deteriorating oxygen sensor may respond slowly, impacting its ability to accurately measure exhaust gases.

– Wiring and connector issues: Damaged or corroded wiring and connectors within the oxygen sensor circuit can hinder proper signal transmission.

– Exhaust leaks: Leaks near the oxygen sensor can introduce false air into the exhaust stream, affecting sensor response.

– ECM communication problems: An ECM malfunction or communication breakdown can lead to delayed sensor data interpretation.

2. Symptoms of DTC P0139:

Recognizing the symptoms associated with DTC P0139 aids mechanics in accurately diagnosing the issue:

– Poor fuel efficiency: Slow oxygen sensor response can lead to inaccurate air-fuel mixture, resulting in increased fuel consumption.

– Rough engine operation: The engine may experience irregular idling or hesitations due to compromised fuel delivery.

– Illuminated Check Engine Light (CEL): DTC P0139 triggers the CEL to alert the driver of a potential problem.

3. Inspection of DTC P0139:

Thorough inspection techniques are essential for accurate diagnosis:

– OBD-II scan: Utilize an OBD-II scanner to retrieve the DTC and accompanying freeze frame data, providing insight into the conditions that activated the code.

– Visual examination: Inspect the oxygen sensor wiring and connectors for visible signs of damage or corrosion.

– Oxygen sensor testing: Measure the sensor’s response time using a scan tool or multimeter.

4. Resolving Causes of DTC P0139:

Addressing DTC P0139 involves specific steps tailored to the underlying issue:

– Oxygen sensor replacement: Replace a sluggish oxygen sensor with a new, high-quality unit that meets manufacturer specifications.

– Wiring and connector repair: Repair or replace damaged wiring and connectors to ensure swift signal transmission.

– Exhaust leak repair: Address any exhaust leaks to prevent the introduction of false air into the exhaust stream.

– ECM diagnosis: If an ECM malfunction is suspected, diagnose and rectify the issue through reprogramming or replacement.

5. Clearing DTC P0139:

After successfully addressing the root cause, clear the DTC from the ECM’s memory using an OBD-II scanner. This step confirms the issue’s resolution and prevents the recurrence of the CEL.


DTC P0139, indicative of slow oxygen sensor response in Bank 1, Sensor 2, underscores the vital role of oxygen sensors in emission control. Through a comprehensive understanding of its causes, recognition of its symptoms, meticulous inspection techniques, and effective solutions, mechanics can accurately diagnose and rectify this issue. Maintaining a responsive oxygen sensor remains pivotal for achieving optimal fuel efficiency, engine performance, and overall vehicle functionality.