my Toyota Corolla E170 (2013-2019) has a P0138 code, what does it mean?

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

Solution

1. Preparation

• Gather tools and ensure the vehicle is on a level surface.
• Disconnect the battery to prevent any electrical shorts.

Tools Required:

• OBD-II scanner
• Multimeter
• Socket set
• Torque wrench
• Safety gloves and goggles

2. Inspect Wiring and Connectors

• Locate the upstream oxygen sensor (typically found on the exhaust manifold or upstream of the catalytic converter).
• Visually inspect the wiring harness and connectors for any signs of wear, fraying, or corrosion.
• If damaged, repair or replace the affected wiring or connectors.

3. Replace Oxygen Sensor

• Remove the old sensor:
  • Use an oxygen sensor socket to loosen and remove the upstream oxygen sensor from the exhaust system.
• Install the new sensor:
  • Apply anti-seize compound to the threads of the new oxygen sensor (if not pre-applied).
  • Screw in the new sensor by hand to avoid cross-threading, then tighten with the socket to the manufacturer’s specified torque (typically 30-40 lb-ft).

4. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0138 trouble code from the vehicle’s computer.

5. Monitor Vehicle Performance

• Start the engine and allow it to reach operating temperature.
• Monitor for any warning lights and ensure the engine runs smoothly.