my Toyota Corolla E170 (2013-2019) has a check engine light and P0420 code, what's causing it?

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, jack and jack stands (or a lift).
• Ensure the vehicle is parked on a level surface and the engine is cool before starting work.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Disconnect the battery to avoid electrical shorts.
  2. Locate the upstream oxygen sensor (before the catalytic converter) and the downstream oxygen sensor (after the catalytic converter).
  3. Use a socket wrench to remove the faulty oxygen sensors, if identified during diagnostics.
  4. Install the new oxygen sensors, ensuring they are tightened to the manufacturer's torque specification (typically around 30 Nm).
  5. Reconnect the battery.

3. Inspect and Replace Catalytic Converter

• Sub-steps:
  1. If the catalytic converter is found to be faulty, raise the vehicle using a jack and secure with jack stands.
  2. Remove the exhaust pipes connected to the catalytic converter using the socket set.
  3. Unbolt the catalytic converter from the exhaust manifold and remove it.
  4. Install the new catalytic converter, ensuring proper alignment with the exhaust system.
  5. Tighten all bolts to the specified torque (consult vehicle service manual for exact values).
  6. Reconnect any exhaust pipes that were removed.

4. Reset Check Engine Light

• Sub-steps:
  1. Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
  2. Disconnect the scanner and start the engine to check if the check engine light remains off.