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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool down completely before starting work.

2. Inspect and Test O2 Sensors

• Tools Required: OBD-II scanner, multimeter
• Sub-steps:
  1. Use the OBD-II scanner to clear the trouble codes.
  2. Reconnect the battery and start the engine.
  3. Allow the engine to reach normal operating temperature.
  4. Use the multimeter to measure the voltage output of the upstream O2 sensor. It should fluctuate between 0.1V and 0.9V.
  5. Measure the downstream O2 sensor voltage. It should be relatively stable.
  6. If the upstream sensor is faulty, replace it with a new one.

3. Check Catalytic Converter

• Tools Required: Jack, jack stands, exhaust pipe cutter (if necessary)
• Sub-steps:
  1. Safely lift the vehicle using a jack and secure it with jack stands.
  2. Inspect the catalytic converter for physical damage, such as cracks or dents.
  3. If the catalytic converter appears clogged, perform a back pressure test to confirm.
  4. If the converter is faulty, remove it by unbolting the flanges and cutting the exhaust pipe if necessary.
  5. Install the new catalytic converter, ensuring proper alignment and sealing.

4. Reconnect and Test

• Sub-steps:
  1. Reconnect all O2 sensors and electrical connections.
  2. Reconnect the battery terminal.
  3. Start the engine and allow it to run for a few minutes.
  4. Use the OBD-II scanner to check for any new codes.