how to fix P0420 code on my GMC Sierra T1XX (2019-Present)

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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on the vehicle.
• Lift the vehicle using a jack and secure it with jack stands.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors (usually found before and after the catalytic converter).
2. Use a socket wrench to remove the oxygen sensors.
3. Inspect the sensor terminals for damage or corrosion.
4. If defective, install new oxygen sensors by reversing the removal process and torqueing to the manufacturer's specifications (typically 30 Nm / 22 lb-ft).
5. Reconnect the battery.

3. Inspect and Replace the Catalytic Converter

1. If the oxygen sensors are functional, inspect the catalytic converter for blockages or damage.
2. Remove the exhaust pipes connected to the catalytic converter using a socket set.
3. Unbolt the catalytic converter from its mounting brackets.
4. Install the new catalytic converter by reversing the removal process, ensuring all bolts are torqued to the manufacturer's specifications (typically 40 Nm / 29 lb-ft).
5. Reattach the exhaust pipes securely.

4. Clear Codes and Test

1. Reconnect the battery if disconnected.
2. Use an OBD-II scanner to clear the P0420 code.
3. Start the engine and allow it to reach operating temperature.