how to fix P0420 code in GMC Sierra T1XX (2019-Present)?

Learn how to diagnose and fix P0420 catalytic converter efficiency issue in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Gather appropriate personal protective equipment (PPE) such as gloves and safety glasses.

2. Inspect and Replace Oxygen Sensors

• Step 1: Remove any engine covers or components blocking access to the upstream and downstream oxygen sensors.
• Step 2: Disconnect the electrical connectors from both the upstream and downstream oxygen sensors.
• Step 3: Use an oxygen sensor socket to remove the sensors from the exhaust manifold and catalytic converter.
• Step 4: Install the new oxygen sensors by hand-tightening them and then torqueing to manufacturer specifications (usually around 30 lb-ft).
• Step 5: Reconnect the electrical connectors to the new oxygen sensors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Step 1: If the catalytic converter is damaged or clogged, it should be replaced. Remove the exhaust pipe bolts using a socket set.
• Step 2: Disconnect any oxygen sensors or exhaust hangers attached to the catalytic converter.
• Step 3: Remove the old catalytic converter from the vehicle.
• Step 4: Install the new catalytic converter, ensuring the inlet and outlet are correctly aligned.
• Step 5: Reinstall the exhaust pipe and oxygen sensors, torqueing the bolts to manufacturer specifications.

4. Reconnect Battery and Clear Codes

• Step 1: Reconnect the negative battery terminal.
• Step 2: Use an OBD-II scanner to clear the P0420 code from the vehicle’s computer.
• Step 3: Start the engine and allow it to reach operating temperature.