how to fix P0420 code in 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 avoid electrical shorts.
• Ensure the vehicle is on a level surface and secure it with jack stands if necessary.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench, multimeter.
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Remove the sensors using the O2 sensor socket.
  4. Test the new sensors with a multimeter to ensure they are functional.
  5. Install the new oxygen sensors, tightening them to the manufacturer’s specifications (typically around 30 lb-ft).
  6. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, exhaust hanger removal tool, torque wrench, penetrating oil.
• Sub-steps:
  1. Inspect the catalytic converter for any visible damage or blockage.
  2. If replacement is necessary, spray penetrating oil on the exhaust bolts and allow it to soak.
  3. Remove the exhaust bolts securing the catalytic converter to the exhaust system and the exhaust manifold.
  4. Use the exhaust hanger removal tool to detach the converter from hangers.
  5. Install the new catalytic converter and tighten the bolts to the manufacturer’s specifications (typically around 25 lb-ft).
  6. Ensure all connections are sealed to prevent leaks.

4. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code.
  3. Take the vehicle for a test drive to monitor performance and check for the check engine light.