how to fix P0420 code on Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to avoid electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Access the Sensors

   • Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
   • Use a socket wrench to remove the sensors from the exhaust system.

2. Test the Sensors

   • Connect a multimeter to each oxygen sensor to check the voltage output.
     • Upstream: should fluctuate between 0.1V to 0.9V.
     • Downstream: should be more stable and less variable.
   • If readings are out of range, replace the faulty sensor.

3. Install New Sensors

   • Apply anti-seize compound on the threads of the new sensors.
   • Install the new sensors and torque them to the manufacturer's specifications (usually around 30 ft-lbs).

3. Inspect and Replace Catalytic Converter

1. Check the Catalytic Converter

   • If the oxygen sensors are functioning correctly, inspect the catalytic converter for signs of damage or clogging.
   • Use a hammer to gently tap the converter; a rattling sound indicates internal damage.

2. Remove the Old Catalytic Converter

   • If replacement is necessary, unbolt the catalytic converter from the exhaust system using a wrench.
   • Remove any heat shields or brackets holding the converter in place.

3. Install the New Catalytic Converter

   • Position the new catalytic converter in place, ensuring proper alignment with the exhaust pipes.
   • Bolt it securely and torque nuts to the specified value (typically around 40 ft-lbs).

4. Reconnect Battery and Clear Codes

1. Reconnect the Battery

   • Reattach the negative battery terminal and ensure it is tight.

2. Clear Diagnostic Codes

   • Use the OBD-II scanner to clear the P0420 code from the ECM.