AutoCodes – Volkswagen – P0138 Volkswagen

P0138 Volkswagen 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 Volkswagen 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.

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Code Popularity 22,089

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

What does this mean?

What are the Possible Causes of the DTC P0138 Volkswagen?

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 Volkswagen?

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 Volkswagen 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 Volkswagen Code

1. What are the common symptoms of OBDII code P0138 in a Volkswagen?

- Common symptoms include poor fuel economy, rough idling, loss of power, and the illumination of the check engine light.

2. What does the HO2S12 sensor circuit high voltage code P0138 indicate in a Volkswagen?

- This code indicates that the oxygen sensor (HO2S12) located after the catalytic converter is sending a high voltage signal to the engine control module.

3. What are the possible causes of the HO2S12 sensor circuit high voltage code P0138 in a Volkswagen?

- Possible causes include a faulty oxygen sensor, wiring issues, exhaust leaks, a malfunctioning catalytic converter, or a problem with the engine control module.

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

- Diagnosing this code typically involves checking the oxygen sensor's voltage output, inspecting the sensor's wiring for damage, and looking for exhaust leaks or other issues in the system.

5. Can I drive my Volkswagen with OBDII code P0138?

- It is not recommended to drive your vehicle with this code as it can lead to poor engine performance and potential damage to the catalytic converter.

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

- Repair options may include replacing the oxygen sensor, repairing any damaged wiring, fixing exhaust leaks, or addressing any other underlying issues causing the high voltage signal.

7. Is it safe to reset the check engine light after fixing OBDII code P0138 in my Volkswagen?

- Yes, once the underlying issue causing the code has been resolved, it is safe to reset the check engine light using an OBDII scanner.

8. How do I prevent OBDII code P0138 from recurring in my Volkswagen?

- Regular maintenance, such as replacing oxygen sensors at recommended intervals, checking for exhaust leaks, and addressing engine issues promptly, can help prevent the code from recurring.

9. Can a DIY enthusiast fix OBDII code P0138 in a Volkswagen?

- Depending on the level of expertise and access to tools, a DIY enthusiast may be able to diagnose and repair this code, but it is recommended to consult a professional if unsure.

10. How much does it cost to fix OBDII code P0138 in a Volkswagen?

- The cost of fixing this code can vary depending on the underlying issue, but it may range from a few hundred to a couple of thousand dollars, including parts and labor.