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 tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent any electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench, multimeter
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Use the O2 sensor socket to remove the upstream sensor first.
  3. Inspect the sensor for damage and replace if necessary.
  4. Repeat the process for the downstream sensor.
  5. Reconnect the battery.

3. Inspect and Replace the Catalytic Converter (if necessary)

• Tools Required: Socket set, jack and jack stands, exhaust gasket, torque wrench
• Sub-steps:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Disconnect the exhaust pipes from the catalytic converter using the socket set.
  3. Remove the mounting bolts securing the catalytic converter to the exhaust manifold.
  4. Remove the old catalytic converter and replace it with a new one, ensuring to use a new gasket.
  5. Reinstall the exhaust pipes and torque the bolts to the manufacturer's specifications.

4. Clear Codes and Test Drive

• Tools Required: OBD-II scanner
• Sub-steps:
  1. Use the OBD-II scanner to clear the P0420 code from the system.
  2. Perform a test drive to ensure that the code does not return and monitor vehicle performance.