AutoCodes – Nissan – P0138 2004 Nissan Altima Sedan

P0138 2004 Nissan Altima Sedan 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 Altima Sedan 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 5,230

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 Altima Sedan 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 Altima Sedan - HO2S12 Circuit High Voltage - AutoCodes.com — P0138 2004 Nissan Altima Sedan Code - HO2S12 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0138 2004 Nissan Altima Sedan?

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 Altima Sedan?

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 Altima Sedan 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 P0138 2004 Nissan Altima Sedan Code

1. What does OBDII code P0138 for a 2004 Nissan Altima Sedan mean?

- OBDII code P0138 on a 2004 Nissan Altima Sedan indicates a fault with the HO2S12 (Heated Oxygen Sensor Bank 1 Sensor 2) circuit, specifically high voltage.

2. What are common symptoms of OBDII code P0138 on a 2004 Nissan Altima Sedan?

- Common symptoms of code P0138 may include decreased fuel efficiency, rough idling, engine hesitation, or an illuminated check engine light on the dashboard.

3. What are possible causes of OBDII code P0138 on a 2004 Nissan Altima Sedan?

- Causes of code P0138 can include a faulty HO2S12 sensor, issues with the wiring or connectors in the sensor circuit, exhaust leaks, or a malfunctioning engine control module (ECM).

4. How do I diagnose OBDII code P0138 on my 2004 Nissan Altima Sedan?

- Diagnosing code P0138 typically involves using a scan tool to check for the specific trouble code, inspecting the HO2S12 sensor and its wiring for damage, and performing tests to verify proper sensor operation.

5. Can I drive my 2004 Nissan Altima Sedan with OBDII code P0138?

- It is generally not recommended to drive your vehicle with an unresolved P0138 code, as it can lead to reduced fuel efficiency and potential damage to the catalytic converter over time.

6. How can I repair OBDII code P0138 on my 2004 Nissan Altima Sedan?

- Repairing code P0138 may involve replacing the HO2S12 sensor, repairing or replacing damaged wiring or connectors, addressing any exhaust leaks, or reprogramming the ECM if necessary.

7. Is it possible to reset OBDII code P0138 on a 2004 Nissan Altima Sedan?

- While you can clear the code using a scan tool, it is important to address the underlying issue causing the P0138 code to prevent it from reoccurring.

8. How much does it cost to fix OBDII code P0138 on a 2004 Nissan Altima Sedan?

- The cost of repairing code P0138 can vary depending on the specific cause of the issue, but it may range from a few hundred to over a thousand dollars, including parts and labor.

9. Can a DIY enthusiast fix OBDII code P0138 on a 2004 Nissan Altima Sedan?

- Depending on your skill level and access to tools, some DIY enthusiasts may be able to address code P0138 themselves by replacing the HO2S12 sensor or fixing wiring issues. However, professional diagnosis and repair are recommended for complex cases.

10. How often does OBDII code P0138 occur in 2004 Nissan Altima Sedans?

- OBDII code P0138 related to the HO2S12 sensor circuit high voltage can occur sporadically in 2004 Nissan Altima Sedans, especially with age and wear on the vehicle components. Regular maintenance and inspections can help prevent this issue.