AutoCodes – Nissan – P0138 2004 Nissan Sentra

P0138 2004 Nissan Sentra 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 2004 Nissan Sentra 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 5,396

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 Jun 14, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0138 2004 Nissan Sentra 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 2004 Nissan Sentra - HO2S12 Circuit High Voltage - AutoCodes.com — P0138 2004 Nissan Sentra Code - HO2S12 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0138 2004 Nissan Sentra?

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 2004 Nissan Sentra?

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 2004 Nissan Sentra 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 2004 Nissan Sentra 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 2004 Nissan Sentra Code

1. What are the common symptoms of OBDII code P0138 on a 2004 Nissan Sentra?

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

2. What does the OBDII code P0138 for a 2004 Nissan Sentra indicate?

- The code P0138 specifically refers to the HO2S12 (Heated Oxygen Sensor Bank 1 Sensor 2) circuit high voltage condition.

3. What are the possible causes of OBDII code P0138 on a 2004 Nissan Sentra?

- Possible causes include a faulty oxygen sensor, wiring issues in the sensor circuit, exhaust system leaks, or a malfunctioning engine control module (ECM).

4. How can I diagnose the cause of OBDII code P0138 on my 2004 Nissan Sentra?

- To diagnose the issue, you can use an OBDII scanner to read the code and check the voltage output of the HO2S12 sensor, inspect the sensor wiring for damage, and look for any exhaust leaks.

5. Can I continue driving my 2004 Nissan Sentra with OBDII code P0138?

- It is not recommended to drive for an extended period with this code as it can lead to poor engine performance and potentially cause damage to the catalytic converter.

6. What is the repair process for OBDII code P0138 on a 2004 Nissan Sentra?

- The repair process involves identifying the root cause (sensor, wiring, or ECM), replacing the faulty component, clearing the code, and performing a test drive to ensure the issue is resolved.

7. How much does it typically cost to fix OBDII code P0138 on a 2004 Nissan Sentra?

- The cost can vary depending on the exact cause of the issue, but it usually ranges from $100 to $300 for parts and labor.

8. Can I reset the Check Engine Light after fixing OBDII code P0138 on my 2004 Nissan Sentra?

- Yes, the Check Engine Light can be reset using an OBDII scanner after the repair is completed to clear the code from the system.

9. How often does OBDII code P0138 occur in 2004 Nissan Sentras?

- While not extremely common, OBDII code P0138 can occur in 2004 Nissan Sentras due to aging sensors, wiring degradation, or other related issues.

10. Is it necessary to visit a mechanic for OBDII code P0138 on a 2004 Nissan Sentra?

- While some DIY enthusiasts may attempt the diagnosis and repair, seeking professional help from a mechanic is recommended to ensure accurate diagnosis and proper resolution of the issue.