AutoCodes – Infiniti – P0138 Infiniti

P0138 Infiniti 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 Infiniti 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 37,421

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
Comments
Add Comment

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

Code P0138 Infiniti 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 Infiniti - HO2S12 Circuit High Voltage - AutoCodes.com — P0138 Infiniti Code - HO2S12 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0138 Infiniti?

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 Infiniti?

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 Infiniti 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 Infiniti code?

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

Need Help with the Code?

Get the P0138 Infiniti code diagnosed by a professional: Find a repair shop in your area

Information for Specific Infiniti Models

P0138 2003 Infiniti G35 — HO2S12 Circuit High Voltage
P0138 2004 Infiniti G35 — HO2S12 Circuit High Voltage
P0138 2005 Infiniti G35 — HO2S12 Circuit High Voltage
P0138 2006 Infiniti G35 — HO2S12 Circuit High Voltage

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 Infiniti Code

No Frequently Asked Questions about P0138 Infiniti Code found.

Discuss the causes and fixes for P0138 Infiniti OBDII Code

Submit a New Comment

Jim
Date: February 12, 2015 at 11:14 pm

Hello I have a 2001 infiniti g20 check code and the code is p0138
I changed the O2 sensor and reset the engine light
After driving approximately 40 miles light came back on
Please help me solve this problem
Thanks

Reply to Comment
OBDIITech
Date: February 12, 2015 at 11:55 pm

Did you used a factory Rear Oxygen Sensor or an aftermarket? did you got the same code P0138? are there any exhaust leaks?

Reply to Comment
Eric
Date: September 6, 2019 at 7:02 am

Hello Autocodes,
I have p0138 and p0139
I haven't replace the O2 B1S2 because I believe it's in good condition. I drive it for couple miles like the previous comment, engine light come up. Any suggestions or solution to solve this issue. Perhaps a video to start somewhere or an idea. I am knowledgeable with automotive. First case scenario, I fail smog check due to bad catalytic converter which is false in my point of view. Especially here in California Emission. Anyways, please reply

Reply to Comment
OBDIITech
Date: September 6, 2019 at 4:07 pm

What model and year is your Infiniti? how did you tested the O2 sensor?
Unless there is an exhaust leak or the catalytic converter is not performing as designed, if you have the P0138 and P0139 code, the most likely cause of the problem is the Rear Oxygen Sensor

Reply to Comment