my Volkswagen Golf MK7 (2015-2019) is showing a P0138 code what does it mean

Volkswagen Golf MK8.5 (2024-Present)

Error Codes

1-3 hours

Time

medium

Difficulty

medium

Severity

Error Code: P0138

3 min read

454 words

Problem Statement

Learn how to diagnose and fix P0138 oxygen sensor circuit issue in Volkswagen Golf MK7. Step-by-step guide with diagnostic procedures and repair instructions.

Error Code

P0138

Affected Component

Exhaust System

Estimated Time

1-3 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical systems to prevent short circuits.

Symptoms

•Check engine light illuminated
•Poor fuel economy
•Engine stalling or rough idle
•Increased emissions
•Lack of power during acceleration

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm the P0138 code.
2
Inspect the wiring and connectors of the upstream oxygen sensor for damage or corrosion.
3
Test the voltage output of the upstream oxygen sensor using a multimeter.
4
Check the vehicle’s fuel trims to see if they are out of range.
5
Inspect the exhaust system for leaks which may affect oxygen sensor readings.

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
•Multimeter
•Socket set
•Torque wrench
•Oxygen sensor socket

Parts Required

•Upstream oxygen sensor

Related Faults

Share this solution

Comments

No comments yet

Be the first to share your thoughts

Back to Generation

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm the P0138 code.
2
Inspect the wiring and connectors of the upstream oxygen sensor for damage or corrosion.
3
Test the voltage output of the upstream oxygen sensor using a multimeter.
4
Check the vehicle’s fuel trims to see if they are out of range.
5
Inspect the exhaust system for leaks which may affect oxygen sensor readings.

Solution

1. Preparation

Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, oxygen sensor socket.
Verify the P0138 code with an OBD-II scanner and document any additional codes.
Disconnect the negative terminal of the battery for safety.

2. Inspect and Repair Wiring

Sub-steps:
1. Locate the upstream oxygen sensor (usually located before the catalytic converter).
2. Inspect the wiring harness and connectors for any signs of fraying, corrosion, or damage.
3. Repair any damaged wires or connections using solder and heat-shrink tubing.
4. Reconnect the wiring harness securely.

3. Test and Replace Oxygen Sensor

Sub-steps:
1. Use a multimeter to test the voltage output of the upstream oxygen sensor; it should range between 0.1V and 0.9V.
2. If the voltage is outside this range or remains constant, proceed to replace the oxygen sensor.
3. Use an oxygen sensor socket to carefully remove the faulty sensor.
4. Install the new oxygen sensor, ensuring the threads are clean and apply anti-seize compound if necessary.
5. Torque the new sensor to the manufacturer’s specifications (typically around 30 Nm).

4. Reset the ECU

Sub-steps:
1. Reconnect the negative battery terminal.
2. Use the OBD-II scanner to clear the trouble codes from the ECU.