AutoCodes – Mazda – P0139 Mazda

P0139 Mazda Code - HO2S RR Circuit Problem

Quick Answer

The Heated Oxygen Sensor 2 (HO2S), after three way catalyst (manifold), monitors the oxygen level in the exhaust gas on each bank. 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 Mazda indicates HO2S RR Circuit Problem.
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.

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Code Popularity 25,067

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 Apr 12, 2019

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0139 Mazda Description

The Heated Oxygen Sensor 2 (HO2S), after three way catalyst (manifold), monitors the oxygen level in the exhaust gas on each bank. For optimum catalyst operation, the air fuel mixture (air-fuel ratio) must be maintained near the ideal stoichiometric ratio. The HO2S output voltage changes suddenly in the vicinity of the stoichiometric ratio. The Engine Control Module (ECM) adjusts the fuel injection time so that the air-fuel ratio is nearly stoichiometric. The HO2S generates a voltage between 0.1 and 0.9 V in response to oxygen in the exhaust gas. If the oxygen in the exhaust gas increases, the air-fuel ratio becomes Lean. The ECM interprets Lean when the HO2S voltage is below 0.45 V. If the oxygen in the exhaust gas decreases, the air-fuel ratio becomes Rich. The ECM interprets Rich when the HO2S voltage is above 0.45 V.

OBDII Code P0139 Mazda - HO2S RR Circuit Problem - AutoCodes.com — P0139 Mazda Code - HO2S RR Circuit Problem

What does this mean?

What are the Possible Causes of the DTC P0139 Mazda?

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
Inappropriate fuel pressure
Faulty fuel injectors
Intake air leaks may be faulty
Exhaust gas leaks

How to Fix the DTC P0139 Mazda?

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

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 Mazda 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 Mazda code?

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Need Help with the Code?

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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 Mazda Code

1. What are the common symptoms of OBDII code P0139 in a Mazda?

- Common symptoms of the P0139 code in a Mazda include poor fuel economy, rough idling, loss of power, and the illumination of the check engine light.

2. What causes the HO2S RR circuit problem in a Mazda?

- The P0139 code in a Mazda is typically caused by issues with the rear oxygen sensor, such as a faulty sensor, damaged wiring, or a poor connection.

3. How serious is the P0139 code in a Mazda?

- While the P0139 code may not cause immediate drivability issues, it can lead to decreased fuel efficiency and potentially harm the catalytic converter if left unresolved.

4. Can I continue driving my Mazda with the P0139 code?

- It is generally not recommended to continue driving your Mazda with the P0139 code, as it can affect the engine's performance and lead to more serious problems over time.

5. How can I diagnose the HO2S RR circuit problem in my Mazda?

- Diagnosing the P0139 code in a Mazda involves using an OBDII scanner to read the trouble code, inspecting the rear oxygen sensor and its wiring, and testing the sensor's functionality.

6. Can I repair the P0139 code in my Mazda myself?

- Depending on your mechanical skills, you may be able to repair the P0139 code in your Mazda yourself by replacing the rear oxygen sensor or repairing any damaged wiring.

7. How much does it cost to fix the P0139 code in a Mazda?

- The cost of fixing the P0139 code in a Mazda can vary depending on the root cause of the issue, but it typically ranges from $100 to $300 for parts and labor.

8. Will resetting the check engine light resolve the P0139 code in my Mazda?

- Simply resetting the check engine light will not fix the underlying issue causing the P0139 code in your Mazda. It is important to diagnose and repair the problem to prevent it from recurring.

9. What is the function of the rear oxygen sensor in a Mazda?

- The rear oxygen sensor in a Mazda monitors the oxygen levels in the exhaust system after the catalytic converter to ensure proper fuel-air mixture and optimal engine performance.

10. Are there any preventative maintenance tips to avoid the P0139 code in a Mazda?

- To prevent the P0139 code in a Mazda, it is recommended to follow the manufacturer's recommended maintenance schedule, use high-quality fuel, and address any engine performance issues promptly.