AutoCodes – Mazda – P0140 Mazda

P0140 Mazda Code - HO2S Rear Circuit No Activity Detected

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: P0140 Mazda indicates HO2S Rear Circuit No Activity Detected.
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 27,289

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
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0140 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 P0140 Mazda - HO2S Rear Circuit No Activity Detected - AutoCodes.com — P0140 Mazda Code - HO2S Rear Circuit No Activity Detected

What does this mean?

What are the Possible Causes of the DTC P0140 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 P0140 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 P0140 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.

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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 P0140 Mazda Code

1. What are the common symptoms of OBDII code P0140 on a Mazda, indicating HO2S Rear Circuit No Activity Detected?

- Common symptoms include poor fuel economy, rough idling, engine misfires, and illuminated Check Engine Light.

2. What are the possible causes of the OBDII code P0140 on a Mazda?

- The code P0140 indicates that the HO2S (Heated Oxygen Sensor) rear circuit is not providing any activity. Possible causes include a faulty oxygen sensor, wiring issues, or a damaged sensor connector.

3. How can I diagnose the issue causing code P0140 on my Mazda?

- To diagnose the issue, you can use an OBDII scanner to check for the specific trouble code. Additionally, you can visually inspect the oxygen sensor and its wiring for any signs of damage.

4. Can a dirty or contaminated oxygen sensor cause code P0140 on a Mazda?

- Yes, a dirty or contaminated oxygen sensor can cause the HO2S Rear Circuit No Activity Detected code P0140. It is recommended to clean or replace the sensor if contamination is suspected.

5. What is the recommended repair for OBDII code P0140 on a Mazda?

- The recommended repair for code P0140 is to diagnose the root cause of the issue, which may involve replacing the rear oxygen sensor, repairing damaged wiring, or fixing a faulty sensor connector.

6. Are there any DIY tips for fixing code P0140 on a Mazda?

- DIY tips include checking and cleaning the sensor connector, inspecting the sensor wiring for damage, and replacing the rear oxygen sensor if necessary. However, if unsure, it's best to consult a professional mechanic.

7. Can driving with OBDII code P0140 on a Mazda cause further damage?

- Continuing to drive with code P0140 may lead to decreased fuel efficiency and potential damage to the catalytic converter. It's advisable to address the issue promptly to prevent further issues.

8. How long does it typically take to repair OBDII code P0140 on a Mazda?

- The repair time for code P0140 can vary depending on the exact cause of the issue. Simple fixes like replacing the oxygen sensor may take around 1-2 hours, while more complex wiring repairs could take longer.

9. Will resetting the Check Engine Light clear OBDII code P0140 on a Mazda?

- Resetting the Check Engine Light may temporarily clear the code, but if the underlying issue causing code P0140 is not addressed, the light is likely to come back on after some time.

10. Is it safe to drive my Mazda with the Check Engine Light on due to code P0140?

- While it may be safe to drive in the short term, it is recommended to address the underlying issue causing code P0140 as soon as possible to prevent potential damage to the vehicle and ensure optimal performance.