why does my Toyota Highlander have a check engine light with code P0420

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the vehicle battery to ensure safety while working on electrical components.

2. Inspect and Replace Oxygen Sensors

• 2.1 Remove the upstream oxygen sensor:
  • Use an O2 sensor socket to unscrew the sensor from the exhaust manifold.
• 2.2 Install the new upstream oxygen sensor:
  • Apply anti-seize compound to the sensor threads if needed.
  • Tighten to the manufacturer’s specifications (often around 30-40 ft-lbs).
• 2.3 Repeat for the downstream oxygen sensor if faulty:
  • Follow the same steps to remove and install.

3. Inspect and Replace Catalytic Converter (if necessary)

• 3.1 Remove exhaust components connected to the catalytic converter:
  • Use a socket set to detach bolts connecting the exhaust pipes.
• 3.2 Inspect the catalytic converter for damage:
  • Look for cracks, dents, or excessive heat damage.
• 3.3 Install the new catalytic converter:
  • Ensure a proper fit and secure all bolts to the manufacturer’s torque specifications (typically 25-35 ft-lbs).

4. Clear Codes and Test Drive

• 4.1 Reconnect the battery and use the OBD-II scanner to clear the check engine light.
• 4.2 Test drive the Highlander to ensure the check engine light does not reappear.