why does my Toyota Corolla E170 (2013-2019) have a check engine light and code P0420?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.
• Allow the engine to cool before beginning work.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream (pre-catalytic) oxygen sensor:
  • Locate the sensor on the exhaust manifold.
  • Use the O2 sensor socket to carefully unscrew the sensor.
• Install the new upstream oxygen sensor:
  • Apply anti-seize compound to the threads of the new sensor.
  • Torque to manufacturer specifications (usually around 30-40 lb-ft).
• Repeat for the downstream (post-catalytic) oxygen sensor if needed.

3. Test Catalytic Converter

• Tools Required: Infrared thermometer
• Start the engine and allow it to reach operating temperature.
• Measure the temperature at the inlet and outlet of the catalytic converter:
  • Inlet temperature should be lower than the outlet temperature by at least 100-150°F.
• If the outlet temperature is not significantly higher, the catalytic converter may need replacement.

4. Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, cutting torch (if welded), exhaust gasket
• Remove the exhaust components connected to the catalytic converter:
  • Unbolt the exhaust pipe from the converter using a socket set.
  • If welded, carefully cut the old converter from the exhaust system.
• Install the new catalytic converter:
  • Position the new converter in place and secure using bolts and a new exhaust gasket.
  • Torque all fasteners to manufacturer specifications.

5. Clear Codes and Test Drive

• Reconnect the battery and clear the fault codes using an OBD-II scanner.
• Start the engine and perform a test drive to ensure the check engine light does not return.