AutoCodes – Nissan – P0138 2009 Nissan Pathfinder

P0138 2009 Nissan Pathfinder Code - HO2S12 Circuit High Voltage

Quick Answer

The Heated Oxygen Sensor 2 (HO2S) (Rear O2 Sensor), 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: P0138 2009 Nissan Pathfinder indicates HO2S12 Circuit High Voltage.
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 2,285

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 Mar 25, 2024

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0138 2009 Nissan Pathfinder Description

The Heated Oxygen Sensor 2 (HO2S) (Rear O2 Sensor), 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 P0138 2009 Nissan Pathfinder - HO2S12 Circuit High Voltage - AutoCodes.com — P0138 2009 Nissan Pathfinder Code - HO2S12 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0138 2009 Nissan Pathfinder?

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
Intake air leaks
Exhaust gas leaks
Inappropriate fuel pressure
Faulty fuel injectors

How to Fix the DTC P0138 2009 Nissan Pathfinder?

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 P0138 2009 Nissan Pathfinder 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 P0138 2009 Nissan Pathfinder 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 P0138 2009 Nissan Pathfinder Code

1. What does the OBDII code P0138 on a 2009 Nissan Pathfinder indicate?

The code P0138 specifically points to an issue with the HO2S12 sensor circuit, indicating high voltage.

2. What are some common symptoms of a HO2S12 Circuit High Voltage error in a 2009 Nissan Pathfinder?

Common symptoms include poor fuel economy, rough idling, engine misfires, and the illumination of the check engine light.

3. What are the possible causes of the HO2S12 Circuit High Voltage error in a 2009 Nissan Pathfinder?

Potential causes include a faulty oxygen sensor, a wiring issue in the sensor circuit, a vacuum leak, or an exhaust system problem.

4. How can I diagnose a HO2S12 Circuit High Voltage issue in my 2009 Nissan Pathfinder?

Diagnosing this issue typically involves using an OBDII scanner to retrieve the specific trouble code, checking the sensor's wiring and connections, and testing the sensor's voltage output.

5. Can driving with a P0138 code on a 2009 Nissan Pathfinder cause any further damage?

Continuing to drive with a HO2S12 Circuit High Voltage error can potentially lead to decreased fuel efficiency, engine performance issues, and damage to the catalytic converter over time.

6. How can I repair a HO2S12 Circuit High Voltage problem in a 2009 Nissan Pathfinder?

Repairing this issue often involves replacing the faulty oxygen sensor, fixing any damaged wiring, addressing vacuum leaks, or repairing exhaust system components.

7. Is it possible to reset the P0138 code on a 2009 Nissan Pathfinder without fixing the underlying issue?

While clearing the code with an OBDII scanner may temporarily turn off the check engine light, the issue will likely reoccur until the root cause is properly addressed.

8. Can a DIY enthusiast tackle the repair of a HO2S12 Circuit High Voltage error in a 2009 Nissan Pathfinder?

Depending on their skill level and tools available, DIYers may be able to replace the oxygen sensor or address wiring issues, but more complex diagnostics and repairs may require professional assistance.

9. How long does it typically take to fix a HO2S12 Circuit High Voltage problem in a 2009 Nissan Pathfinder?

The repair time can vary based on the exact cause of the issue and the expertise of the person performing the repair, but it can range from a quick sensor replacement to a more involved troubleshooting process.

10. Will fixing the HO2S12 Circuit High Voltage error improve the overall performance of a 2009 Nissan Pathfinder?

Repairing this issue can help restore proper fuel efficiency, engine operation, and emissions control in the vehicle, leading to improved overall performance.