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

Learn how to diagnose and fix P0420 code for GMC Sierra T1XX. Step-by-step guide with symptoms, diagnostic steps, tools, and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle's battery.
• Ensure the vehicle is on a level surface and use wheel chocks for safety.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set
• Remove the O2 sensor located upstream (pre-catalytic converter).
  • Sub-step 1: Disconnect the electrical connector.
  • Sub-step 2: Use the O2 sensor socket to unscrew and remove the sensor.
• Install the new O2 sensor.
  • Sub-step 1: Apply anti-seize compound (if applicable) to the threads of the new sensor.
  • Sub-step 2: Screw the new sensor in place and reconnect the electrical connector.

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

• Tools Required: Socket set, torque wrench, exhaust pipe cutter
• Remove the catalytic converter.
  • Sub-step 1: Use the socket set to unbolt the catalytic converter from the exhaust manifold and exhaust pipe.
  • Sub-step 2: Cut the exhaust pipes if they are welded (if applicable) and remove the old converter.
• Install the new catalytic converter.
  • Sub-step 1: Position the new converter in place and secure it with bolts.
  • Sub-step 2: Torque the bolts to the manufacturer's specifications (check service manual for specific torque values).

4. Reconnect Battery and Clear Codes

• Reconnect the vehicle's battery.
• Use an OBD-II scanner to clear the P0420 code from the system.