how to fix the P0138 oxygen sensor code on my Volkswagen Golf MK7 (2015-2019)?

Volkswagen Golf MK8.5 (2024-Present)

Error Codes

1-2 hours

Time

medium

Difficulty

medium

Severity

Error Code: P0138

3 min read

497 words

Problem Statement

Learn how to diagnose and fix P0138 oxygen sensor code in Volkswagen Golf MK7 (2015-2019). Step-by-step guide with diagnostic procedures and repair instructions.

Error Code

P0138

Affected Component

Exhaust System

Estimated Time

1-2 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical systems.
•Allow the engine to cool before working on the exhaust system.

Symptoms

•Check engine light illuminated
•Rough idle or stalling
•Decreased fuel economy
•Increased emissions
•Poor acceleration or hesitation during acceleration

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0138 and check for any additional codes.
2
Inspect the wiring and connector to the oxygen sensor for damage, corrosion, or loose connections.
3
Measure the voltage output of the oxygen sensor using a multimeter while the engine is running.
4
Check the vehicle’s fuel trim readings to determine if they are out of range.
5
Inspect the exhaust system for leaks that could affect sensor readings.
6
Ensure that the engine is operating at the correct temperature, as a faulty thermostat can affect sensor performance.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•OBD-II scanner
•Oxygen sensor socket
•Multimeter
•Wrench set
•Torque wrench

Parts Required

•New upstream oxygen sensor
•Anti-seize compound (if not pre-applied)

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Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0138 and check for any additional codes.
2
Inspect the wiring and connector to the oxygen sensor for damage, corrosion, or loose connections.
3
Measure the voltage output of the oxygen sensor using a multimeter while the engine is running.
4
Check the vehicle’s fuel trim readings to determine if they are out of range.
5
Inspect the exhaust system for leaks that could affect sensor readings.
6
Ensure that the engine is operating at the correct temperature, as a faulty thermostat can affect sensor performance.

Solution

1. Preparation

Gather tools and parts required for the repair.
Disconnect the negative terminal of the battery to ensure safety.

2. Remove the Oxygen Sensor

Locate the upstream oxygen sensor (typically near the exhaust manifold).
Use an oxygen sensor socket to unscrew the sensor from the exhaust pipe.
Disconnect the electrical connector from the oxygen sensor.

3. Inspect and Clean

Inspect the sensor threads for damage and clean the area surrounding the sensor to prevent debris from entering the exhaust system.
If the wiring or connector is damaged, repair or replace them as necessary.

4. Install New Oxygen Sensor

Apply anti-seize compound to the threads of the new oxygen sensor (if not pre-applied).
Install the new oxygen sensor into the exhaust pipe and tighten it to the manufacturer’s specifications (usually around 30 Nm).
Reconnect the electrical connector to the new sensor.

5. Reconnect Battery and Test

Reconnect the negative terminal of the battery.
Start the engine and allow it to reach operating temperature.
Use the OBD-II scanner to clear the P0138 code and check if it returns after a test drive.