how to fix P0420 code on 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 necessary tools and parts.
• Disconnect the negative terminal of the battery to avoid electrical shorts.
• Allow the exhaust system to cool down before working on it.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, penetrating oil.
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors on the exhaust system.
  2. Use penetrating oil on the sensor threads and allow it to soak for a few minutes.
  3. Disconnect the electrical connectors from both sensors.
  4. Remove the sensors using the O2 sensor socket.
  5. Install the new sensors by threading them in by hand, then torque to manufacturer specifications (typically around 30 lb-ft).
  6. Reconnect the electrical connectors.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if necessary).
• Sub-steps:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Inspect the catalytic converter for visible damage or blockage.
  3. If replacement is necessary, disconnect any exhaust clamps or bolts securing the catalytic converter to the exhaust system.
  4. Cut the exhaust pipe if needed to remove the old catalytic converter.
  5. Install the new catalytic converter, ensuring it is oriented correctly.
  6. Secure the converter with clamps or bolts, torquing to manufacturer specifications.

4. Clear Codes and Test Drive

• 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 system.
  3. Start the engine and allow it to reach operating temperature.
  4. Take the vehicle for a test drive, ensuring to monitor the engine's performance and emissions.