how to troubleshoot P0420 code on Toyota Highlander XU70 (2020-Present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.

2. Inspect and Replace Oxygen Sensors

1. Locate the O2 sensors: Identify the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
2. Remove the sensors: Use an O2 sensor socket to carefully unscrew the sensors from their mounting points.
3. Test the sensors: Use a multimeter to check the resistance and output voltage of both sensors, ensuring they are within specifications (typically 0.1 to 0.9 volts for the upstream sensor).
4. Replace faulty sensors: If either sensor is out of spec, replace it with a new, OEM-quality part.
5. Reinstall sensors: Screw the new sensors back into place and torque them to the manufacturer’s specifications (usually around 30 lb-ft).

3. Inspect and Replace Catalytic Converter (if necessary)

1. Visual inspection: Check the catalytic converter for any signs of physical damage or excessive heat (discoloration, rattling).
2. Test for flow restriction: Use a backpressure gauge to measure exhaust backpressure. It should not exceed 2.5 psi at 2,500 RPM.
3. Replace the catalytic converter: If restricted, remove the old converter by unbolting it from the exhaust pipes using a socket set. Ensure to replace any gaskets or seals.
4. Install new catalytic converter: Position the new unit, align it, and secure it with the provided hardware. Torque bolts to manufacturer specifications.
5. Reconnect the battery: Once all components are replaced, reconnect the battery.