how to fix P0420 catalyst system efficiency below threshold on Toyota Highlander Fourth Generation (...

Solution

1. Preparation

• Tools Needed: OBD-II scanner, multimeter, socket set, torque wrench, exhaust back pressure gauge, safety glasses, gloves.
• Disconnect the negative battery terminal to avoid electrical shorts.

2. Oxygen Sensor Replacement (if faulty)

1. Locate the Sensors: Identify the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Remove the Sensors: Use the appropriate socket to unscrew the faulty oxygen sensors from their locations.
3. Install New Sensors: Apply anti-seize compound on the threads of the new sensors, then install and tighten them to the manufacturer's specified torque (usually around 30-40 lb-ft).
4. Reconnect Wiring: Ensure all wiring harnesses are secure and properly connected.

3. Catalytic Converter Replacement (if damaged)

1. Remove Exhaust Components: Detach any exhaust components connected to the catalytic converter, such as the exhaust pipe or brackets, using a socket set.
2. Extract the Catalytic Converter: Carefully remove the old catalytic converter from its mounting points and set it aside.
3. Install New Catalytic Converter: Position the new catalytic converter in place and align it with the exhaust pipes.
4. Secure the Converter: Tighten all bolts and clamps to the manufacturer’s torque specifications.
5. Reconnect Exhaust Components: Reattach any exhaust components previously removed, ensuring all connections are secure.

4. Reset the Engine Control Module (ECM)

1. Reconnect Battery Terminal: Reconnect the negative battery terminal once all repairs are complete.
2. Clear Error Codes: Use the OBD-II scanner to clear the P0420 code from the ECM.