AutoCodes – Nissan – P0138 2003 Nissan Sentra

P0138 2003 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 2003 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 4,779

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 2003 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 2003 Nissan Sentra - HO2S12 Circuit High Voltage - AutoCodes.com — P0138 2003 Nissan Sentra Code - HO2S12 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0138 2003 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 2003 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 2003 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.

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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 2003 Nissan Sentra Code

1. What does the OBDII code P0138 for a 2003 Nissan Sentra mean?

The code P0138 indicates a high voltage condition in the downstream oxygen sensor (HO2S12) circuit of the exhaust system.

2. What are the common symptoms of OBDII code P0138 in a 2003 Nissan Sentra?

Common symptoms of code P0138 in a 2003 Nissan Sentra may include poor fuel economy, rough idling, engine stalling, and the illumination of the "Check Engine" light on the dashboard.

3. What are the possible causes of OBDII code P0138 on a 2003 Nissan Sentra?

Potential causes of code P0138 in a 2003 Nissan Sentra include a faulty oxygen sensor, wiring issues in the sensor circuit, exhaust leaks, or a malfunctioning engine control module (ECM).

4. How can I diagnose OBDII code P0138 in my 2003 Nissan Sentra?

To diagnose code P0138, you can use an OBDII scanner to retrieve the code and then inspect the oxygen sensor, wiring connections, and the ECM for any visible damage or defects.

5. How do I repair OBDII code P0138 on a 2003 Nissan Sentra?

Repairing code P0138 may involve replacing the downstream oxygen sensor (HO2S12), repairing any damaged wiring, fixing exhaust leaks, or reprogramming the ECM to address the high voltage issue.

6. Can I drive my 2003 Nissan Sentra with OBDII code P0138?

It is not recommended to drive your 2003 Nissan Sentra with an unresolved P0138 code, as it can lead to decreased fuel efficiency and potential damage to the catalytic converter over time.

7. How much does it cost to fix OBDII code P0138 on a 2003 Nissan Sentra?

The cost to fix code P0138 on a 2003 Nissan Sentra can vary depending on the specific issue causing the code. Replacement oxygen sensors can range from $50 to $200, while professional labor costs may add to the total repair bill.

8. Will resetting the check engine light resolve OBDII code P0138 on a 2003 Nissan Sentra?

Simply resetting the check engine light will not fix the underlying issue causing code P0138. It is important to diagnose the problem, make the necessary repairs, and then clear the code using an OBDII scanner.

9. How often does OBDII code P0138 occur in a 2003 Nissan Sentra?

Code P0138 can occur sporadically or persistently in a 2003 Nissan Sentra, depending on the severity of the issue causing the high voltage condition in the downstream oxygen sensor circuit.

10. Can a DIY mechanic fix OBDII code P0138 on a 2003 Nissan Sentra?

A DIY mechanic with the necessary tools and knowledge about oxygen sensors and electrical systems may be able to diagnose and repair code P0138 in a 2003 Nissan Sentra. However, if in doubt, it is recommended to seek professional assistance for accurate diagnosis and repair.