how to fix P0420 code on my Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical issues.
• Allow the vehicle to cool down if the engine was running.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench, multimeter.
• Remove the upstream (pre-catalytic converter) oxygen sensor.
  • Use the O2 sensor socket to unscrew the sensor.
  • Disconnect the electrical connector.
• Test the sensor's resistance with a multimeter.
• If faulty, replace it with a new sensor (ensure it meets OEM specifications).
• Reinstall the new oxygen sensor and reconnect the electrical connector.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, torque wrench, penetrating oil.
• Locate the catalytic converter and inspect it for any signs of damage or blockage.
• If necessary, remove the catalytic converter:
  • Unbolt the exhaust flanges using a socket set.
  • If bolts are rusted, apply penetrating oil and allow it to soak.
• Install the new catalytic converter:
  • Align it properly and secure it using the original bolts or new ones as needed.
  • Torque the bolts to the manufacturer's specifications.

4. Clear Codes and Test Drive

• Reconnect the negative battery terminal.
• Use an OBD-II scanner to clear the P0420 code from the ECU.
• Test drive the vehicle for at least 20 minutes, monitoring performance and ensuring no new codes appear.