how to diagnose and fix P0420 code on Toyota Corolla E170 (2013-2019)

Solution

1. Preparation

• Tools Needed: OBD-II scanner, multimeter, socket set, torque wrench, safety goggles, gloves.
• Safety Warning: Disconnect the battery before starting work on electrical systems.

2. Inspect and Replace Oxygen Sensors (if necessary)

• Sub-steps:
  1. Disconnect the upstream and downstream oxygen sensors.
  2. Use a multimeter to test the sensors’ output voltage; replace if readings are out of specifications (typically around 0.1 to 0.9 volts for a functioning sensor).
  3. Install new sensors by threading them into their respective locations and tightening them to the manufacturer’s torque specifications (generally around 30 ft-lbs).

3. Inspect and Clean/Replace Catalytic Converter

• Sub-steps:
  1. Remove the catalytic converter by loosening the bolts or nuts securing it to the exhaust system using a socket set.
  2. Inspect the catalytic converter for internal damage or blockage; if damaged, replace it with an OEM or high-quality aftermarket part.
  3. If cleaning is warranted (only if not physically damaged), use a specialized catalytic converter cleaner as per instructions, or consider professional cleaning.

4. Reassemble Exhaust Components

• Sub-steps:
  1. Reinstall the catalytic converter (if cleaned or replaced) and secure it with the bolts/nuts to the specified torque.
  2. Reconnect the oxygen sensors and ensure all electrical connections are secure.

5. Clear Error Codes and Test Drive

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code.
  3. Perform a test drive to allow the vehicle to go through its monitoring cycle and check if the check engine light reappears.