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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety.
• Raise the vehicle using a jack and secure with jack stands.

2. Inspect and Repair Exhaust System

• Tools Required: Socket set, exhaust pipe wrench.
• Sub-steps:
  1. Inspect the entire exhaust system for leaks or damage, particularly around the catalytic converter.
  2. If any leaks are found, repair or replace the damaged section using appropriate exhaust sealant or clamps.

3. Test and Replace Oxygen Sensors (if necessary)

• Tools Required: O2 sensor socket, multimeter.
• Sub-steps:
  1. Remove the upstream and downstream oxygen sensors using the O2 sensor socket.
  2. Test the sensors with a multimeter; compare readings with manufacturer specifications.
  3. If any sensor fails the test, replace it with a new one, ensuring proper torque when installing (typically around 30 ft-lbs).

4. Catalytic Converter Inspection

• Tools Required: Temperature gauge, torque wrench.
• Sub-steps:
  1. Use a temperature gauge to measure the temperature of the exhaust gas entering and exiting the catalytic converter.
  2. If the outlet temperature is significantly lower than the inlet (more than 100°F difference), the catalytic converter may be failing.
  3. If necessary, replace the catalytic converter following manufacturer specifications and using a torque wrench to secure bolts to the recommended torque (usually around 40-50 ft-lbs).