AutoCodes – Mercedes-Benz – P0139 Mercedes-Benz

P0139 Mercedes-Benz Code - O2 Sensor Circuit Slow Response Bank 1 Sensor 2

Quick Answer

This fault code is stored in the Engine Control Module (ECM) when the output from the exhaust gas oxygen sensor is not as expected. Common causes include Faulty Rear Heated Oxygen Sensor Bank 1, Rear Heated Oxygen Sensor Bank 1 harness is open or shorted, Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

What it means: P0139 Mercedes-Benz indicates O2 Sensor Circuit Slow Response Bank 1 Sensor 2.
Common causes: Common causes include Faulty Rear Heated Oxygen Sensor Bank 1, Rear Heated Oxygen Sensor Bank 1 harness is open or shorted, Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection.
Severity: Moderate - service should be scheduled soon.
Can I drive?: The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

Save to My Repairs Step-by-Step Diagnostic Guide My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 7,104

How popular is this code, among other codes? Low

Repair Importance Level

Moderate (Service soon) (2 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Sep 15, 2019

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code P0139 Mercedes-Benz Description

This fault code is stored in the Engine Control Module (ECM) when the output from the exhaust gas oxygen sensor is not as expected. The engine control module analyses the signal generated from the exhaust gas oxygen sensor to monitor how quickly the sensor can switch from one condition to another. An example of this is a voltage shift from a low voltage to a high voltage during full load enrichment. Another example is a voltage shift from a high voltage to a low voltage during over-run fuel shutoff. With a narrow-band oxygen sensor a low voltage indicates a lean mixture and a high voltage indicates a rich mixture. Narrow-band oxygen sensors can only act as a rich or lean indicator. They cannot measure the actual air/fuel ratio. A wide-band oxygen sensor is required to measure actual air/fuel ratio. A normal allowable time to shift from lean to rich is approximately 100 milliseconds. A normal allowable time to shift from rich to lean is approximately 150 milliseconds. The response of the oxygen sensor should be measured using an oscilloscope rather than scantool live data. This is due to the scantool receiving data from the engine control module which has already been processed so the data may seem slower when displayed on the scantool.

OBDII Code P0139 Mercedes-Benz - O2 Sensor Circuit Slow Response Bank 1 Sensor 2 - AutoCodes.com — P0139 Mercedes-Benz Code - O2 Sensor Circuit Slow Response Bank 1 Sensor 2

What does this mean?

What are the Possible Causes of the DTC P0139 Mercedes-Benz?

Faulty Rear Heated Oxygen Sensor Bank 1
Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection

How to Fix the DTC P0139 Mercedes-Benz?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

Mercedes Benz Code = 0511 (Right O2 sensor, after TWC): Aging (P0139)

Replacing the Rear Heated Oxygen Sensor Bank 1 usually takes care of the problem.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0139 Mercedes-Benz code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0139 Mercedes-Benz code?

Need more information on how to fix the P0139 Mercedes-Benz code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0139 Mercedes-Benz code diagnosed by a professional: Find a repair shop in your area

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0139 Mercedes-Benz Code

1. What does the OBDII code P0139 mean on a Mercedes-Benz?

P0139 indicates that the O2 Sensor Circuit Slow Response in Bank 1 Sensor 2 is not functioning as expected, suggesting that the sensor's response to changes in oxygen levels is slower than normal.

2. Where is Bank 1 Sensor 2 located on a Mercedes-Benz?

Bank 1 refers to the side of the engine that contains the first cylinder, and Sensor 2 is the oxygen sensor located downstream or after the catalytic converter.

3. What are common symptoms of the P0139 code in a Mercedes-Benz?

Symptoms include a check engine light, poor fuel economy, rough engine idle, and potentially a noticeable drop in engine performance.

4. What could cause the O2 sensor to respond slowly, triggering the P0139 code?

Causes could include a faulty oxygen sensor, exhaust leaks, damaged or corroded wiring or connectors, or a malfunctioning catalytic converter.

5. How can I fix the P0139 code on my Mercedes-Benz?

Repair strategies include replacing the faulty oxygen sensor, repairing any exhaust leaks, checking and repairing damaged wiring, and if necessary, replacing the catalytic converter.

6. Is it safe to drive my Mercedes-Benz with the P0139 code?

While you can typically still drive the vehicle, it is advisable to address the issue promptly as it can lead to increased emissions, reduced fuel efficiency, and potential damage to the catalytic converter.

7. How do I verify that the new O2 sensor has resolved the P0139 code on my Mercedes-Benz?

After replacing the sensor, clear the diagnostic trouble codes from your vehicleâ€™s computer and drive the car for a while to see if the check engine light reappears and to ensure the repair was successful.

8. What tools are needed to diagnose and repair the P0139 code on a Mercedes-Benz?

Tools needed might include an OBDII code reader, digital multimeter, and basic hand tools to access and replace the oxygen sensor.

9. Could a P0139 code result from using low-quality fuel in my Mercedes-Benz?

While low-quality fuel might contribute to engine performance issues, it's unlikely to be a direct cause of a slow response from an O2 sensor. However, consistent use of poor-quality fuel can lead to engine deposits that might affect overall vehicle performance.

10. What is the cost implication of fixing the P0139 code in a Mercedes-Benz?

The cost primarily depends on whether you need to replace the sensor or perform additional repairs like fixing exhaust leaks or replacing the catalytic converter. Oxygen sensor replacement can range from $200 to $400 including parts and labor.