how to fix P0420 code on my Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety while working on electrical components.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic converter) oxygen sensor and the downstream (post-catalytic converter) oxygen sensor.
  2. Use an O2 sensor socket to remove the upstream sensor; ensure to replace it if faulty.
  3. Repeat the process for the downstream sensor.
  4. Install new sensors and torque them to manufacturer specifications (typically around 30 ft-lbs).

3. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. If the catalytic converter is found to be faulty (evidenced by temperature difference or other diagnostics), remove any heat shields.
  2. Use a socket set to unbolt the catalytic converter from the exhaust manifold and the exhaust pipe.
  3. Install the new catalytic converter, ensuring proper alignment and sealing.
  4. Torque the bolts to manufacturer specifications (usually around 30-35 ft-lbs).
  5. Reinstall heat shields, if applicable.

4. Reconnect Battery and Test

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Start the vehicle and allow it to reach operating temperature.
  3. Check for any error codes using the OBD-II scanner.