AutoCodes – Nissan – P0138 2004 Nissan Maxima

P0138 2004 Nissan Maxima 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 Maxima 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.

Save to My Repairs Step-by-Step Diagnostic Guide My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 8,871

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
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

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

What does this mean?

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

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 Maxima?

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 Maxima 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 Maxima code?

Need more information on how to fix the P0138 2004 Nissan Maxima code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0138 2004 Nissan Maxima code diagnosed by a professional: Find a repair shop in your area

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 Maxima Code

1. What does OBDII code P0138 on my 2004 Nissan Maxima mean?

Code P0138 indicates that the HO2S12 (Heated Oxygen Sensor 2 Bank 1 Sensor 2) circuit is registering high voltage.

2. What are the common symptoms of OBDII code P0138 on a 2004 Nissan Maxima?

Common symptoms include decreased fuel efficiency, rough idling, engine misfires, and the illumination of the Check Engine Light.

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

Potential causes include a faulty oxygen sensor, wiring or connector issues, exhaust leaks, engine misfires, or a malfunctioning ECM (Engine Control Module).

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

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

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

It's not recommended to continue driving with a P0138 code, as it can lead to further damage to the engine and emissions system. It's best to address the issue promptly.

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

Repair options may include replacing the HO2S12 sensor, repairing damaged wiring or connectors, fixing exhaust leaks, addressing engine misfires, or reprogramming the ECM.

7. Is it safe to reset the Check Engine Light after fixing OBDII code P0138 on a 2004 Nissan Maxima?

Yes, once the underlying issue causing P0138 is resolved, it's safe to reset the Check Engine Light using an OBDII scanner.

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

The cost of repair can vary depending on the exact cause of the issue. Replacing the oxygen sensor can range from $100 to $300, while addressing wiring or other problems may increase the cost.

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

Depending on their skills and tools, a DIY enthusiast may be able to address some causes of P0138, such as replacing the oxygen sensor. However, more complex issues may require professional assistance.

10. How often does OBDII code P0138 occur in 2004 Nissan Maxima vehicles?

While not extremely common, P0138 can occur in 2004 Nissan Maxima vehicles due to various factors affecting the oxygen sensor and its circuitry. Regular maintenance can help prevent such issues.