AutoCodes – Audi – P0138 Audi

P0138 Audi Code - HO2S12 Sensor 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 Audi indicates HO2S12 Sensor 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 12,036

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 Audi 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 Audi - HO2S12 Sensor Circuit High Voltage - AutoCodes.com — P0138 Audi Code - HO2S12 Sensor Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0138 Audi?

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 Audi?

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 Audi 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 Audi code?

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

Need Help with the Code?

Get the P0138 Audi 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 Audi Code

1. What are the common symptoms of OBDII code P0138 in an Audi?

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

2. What does the OBDII code P0138 Audi HO2S12 Sensor Circuit High Voltage indicate?

- This code indicates that the oxygen sensor (HO2S12) located downstream of the catalytic converter is reporting a high voltage reading.

3. What are the possible causes of OBDII code P0138 in an Audi?

- The possible causes include a faulty oxygen sensor, wiring issues in the sensor circuit, exhaust leaks, engine misfires, or a malfunctioning catalytic converter.

4. How can I diagnose the cause of OBDII code P0138 in my Audi?

- Diagnosis typically involves inspecting the oxygen sensor and its wiring, checking for exhaust leaks, scanning for any additional trouble codes, and performing a voltage test on the sensor.

5. Can I drive my Audi with the OBDII code P0138 present?

- It is generally not recommended to drive with this code present, as it can lead to decreased fuel efficiency and potential damage to the catalytic converter over time.

6. How can I repair OBDII code P0138 in my Audi?

- Repair may involve replacing the HO2S12 sensor, repairing any wiring issues, fixing exhaust leaks, addressing engine misfires, or replacing the catalytic converter if necessary.

7. Are there any maintenance tips to prevent OBDII code P0138 from recurring?

- Regularly inspecting and replacing oxygen sensors at recommended intervals, addressing engine performance issues promptly, and ensuring proper exhaust system maintenance can help prevent this code from recurring.

8. Will resetting the Check Engine Light resolve OBDII code P0138 in my Audi?

- Resetting the Check Engine Light may temporarily clear the code, but it will not fix the underlying issue causing the high voltage reading from the oxygen sensor.

9. Can a DIY enthusiast repair OBDII code P0138 in an Audi?

- Depending on the cause, some DIY enthusiasts may be able to repair this code themselves, especially if it involves replacing the oxygen sensor or addressing minor wiring issues.

10. How crucial is it to address OBDII code P0138 promptly in an Audi?

- It is important to address this code promptly to prevent potential damage to the catalytic converter, ensure optimal engine performance, and maintain fuel efficiency.