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.
• Ensure the vehicle is parked on a level surface and the engine is cool.

2. Replace Oxygen Sensors (if needed)

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Sub-steps:
  1. Disconnect the negative battery terminal.
  2. Locate the pre-catalytic and post-catalytic oxygen sensors.
  3. Use the O2 sensor socket to remove the sensors.
  4. Install the new sensors by threading them in by hand, then torque to the manufacturer’s specification (typically around 30 lb-ft).
  5. Reconnect the O2 sensor connectors.

3. Inspect/Replace Catalytic Converter (if needed)

• Tools Required: Socket set, torque wrench, exhaust pipe cutter or saw (if necessary)
• Sub-steps:
  1. Inspect the catalytic converter for physical damage or obstruction.
  2. If replacement is necessary, use the exhaust pipe cutter to remove the old catalytic converter.
  3. Install the new catalytic converter, ensuring proper alignment and sealing.
  4. Torque the exhaust bolts to manufacturer's specifications (consult service manual, typically around 35-45 lb-ft).
  5. Reconnect any exhaust hangers and verify there are no leaks.

4. Clear Codes and Test

• Tools Required: OBD-II scanner
• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code from the engine control module (ECM).
  3. Start the engine and let it reach operating temperature.
  4. Take the vehicle for a test drive to ensure the check engine light does not return.