AutoCodes – Subaru – P0140 Subaru

P0140 Subaru Code - HO2S12 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 Subaru indicates HO2S12 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 24,498

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 Subaru 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 Subaru - HO2S12 No Activity Detected - AutoCodes.com — P0140 Subaru Code - HO2S12 No Activity Detected

What does this mean?

What are the Possible Causes of the DTC P0140 Subaru?

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 Subaru?

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 Subaru 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 Subaru Code

1. What are the common symptoms of OBDII code P0140 in a Subaru?

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

2. What does the OBDII code P0140 Subaru - HO2S12 No Activity Detected mean?

- This code indicates that the oxygen sensor (HO2S12) located after the catalytic converter is not sending any signals or is not functioning properly.

3. What are the possible causes of the HO2S12 No Activity Detected error code?

- Common causes include a faulty oxygen sensor, damaged wiring or connectors, exhaust leaks, or issues with the engine's air-fuel mixture.

4. How can I diagnose the issue causing the P0140 code in my Subaru?

- To diagnose the problem, you can use an OBDII scanner to read the code, visually inspect the oxygen sensor and its connections, check for exhaust leaks, and perform voltage tests on the sensor.

5. Can I continue driving my Subaru with the P0140 code present?

- It is not recommended to drive with the P0140 code as it can lead to decreased fuel efficiency and potential damage to the catalytic converter over time.

6. How can I repair the HO2S12 No Activity Detected issue in my Subaru?

- Repair options may include replacing the oxygen sensor, repairing damaged wiring or connectors, fixing exhaust leaks, and ensuring the air-fuel mixture is within the correct parameters.

7. Are there any DIY tips for resolving the P0140 error code in a Subaru?

- DIY tips may include checking and cleaning the oxygen sensor connections, inspecting the sensor for physical damage, and ensuring there are no exhaust leaks in the system.

8. How much does it typically cost to fix the OBDII code P0140 in a Subaru?

- The cost of repairs can vary depending on the specific issue, but replacing an oxygen sensor can range from $100 to $300, while addressing exhaust leaks or wiring problems may incur additional costs.

9. Can a P0140 error code be triggered by issues other than the oxygen sensor?

- Yes, other issues such as exhaust leaks, wiring problems, or issues with the engine's air-fuel mixture can also trigger the P0140 code in a Subaru.

10. How often should I have my Subaru's oxygen sensors inspected to prevent the P0140 code from occurring?

- It is recommended to have your oxygen sensors inspected during routine maintenance intervals, typically every 30,000 to 50,000 miles, to help prevent issues like the P0140 code from occurring.