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

Learn how to diagnose and fix P0420 catalytic converter issues in GMC Sierra T1XX (2019-Present). Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Tools Required:
  • OBD-II scanner
  • Socket set
  • Torque wrench
  • Multimeter
  • Exhaust backpressure gauge
• Ensure the vehicle is parked on a level surface and the parking brake is engaged. Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors (if necessary)

• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors on the exhaust system.
  2. Disconnect the electrical connectors from both sensors.
  3. Remove the sensors using a socket or appropriate wrench.
  4. Install new oxygen sensors (if faulty) by threading them into the exhaust system and tightening to the manufacturer’s torque specifications.
  5. Reconnect the electrical connectors ensuring a secure fit.

3. Replace the Catalytic Converter (if necessary)

• Sub-steps:
  1. Locate the catalytic converter in the exhaust system.
  2. Remove any heat shields or brackets securing the catalytic converter.
  3. Disconnect the exhaust pipes connected to the catalytic converter using a socket set.
  4. Remove the catalytic converter from its mounting.
  5. Install the new catalytic converter by reversing the removal steps, ensuring all connections are tight and secure.

4. Clear Codes and Test

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear any stored codes.
  3. Start the engine and allow it to reach operating temperature.
  4. Monitor the vehicle’s performance and scan for any reoccurring codes.