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

Learn how to diagnose and resolve P0420 code related to catalytic converter efficiency in GMC Sierra T1XX. Step-by-step guide with diagnostic and repair instructions.

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors by:
  1. Using the O2 sensor socket to loosen and remove the sensors.
  2. Inspecting the old sensors for damage or contamination.
  3. Installing new sensors and tightening them to the manufacturer's torque specifications (typically around 30 lb-ft).
• Reconnect the battery.

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

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if applicable)
• If the catalytic converter is damaged or inefficient:
  1. Raise the vehicle and secure it on jack stands.
  2. Disconnect the exhaust pipes from the catalytic converter.
  3. Remove any mounting bolts or brackets securing the converter.
  4. Install the new catalytic converter, ensuring proper alignment and sealing.
  5. Reattach the exhaust pipes and tighten all connections.

4. Clear Codes and Test Drive

• Use the OBD-II scanner to clear the P0420 code.
• Test drive the vehicle for at least 20-30 minutes to ensure the code does not reappear.