how to fix P0420 code on my 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

• Tools Required: OBD-II scanner, multimeter, socket set, safety goggles, gloves
• Disconnect the battery before starting work on the exhaust system.
• Allow the engine to cool before proceeding.

2. Inspect and Repair Exhaust System

• Sub-steps:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Visually inspect the entire exhaust system for leaks, cracks, or loose connections.
  3. If any leaks are found, repair them by welding or replacing the affected sections of the exhaust.

3. Check and Replace Oxygen Sensors (if necessary)

• Sub-steps:
  1. Use the wrench to remove the downstream oxygen sensor from the exhaust pipe.
  2. Compare the readings from the multimeter against the manufacturer specifications.
  3. If the sensor is faulty, install a new oxygen sensor by reversing the removal process.
  4. Ensure to torque the sensor to the manufacturer’s specification (usually around 30 lb-ft).

4. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. If the catalytic converter is blocked or damaged, remove it by unscrewing the bolts securing it to the exhaust system.
  2. Install a new catalytic converter, ensuring proper alignment and sealing with gaskets.
  3. Torque the bolts to the manufacturer’s specification (typically around 40-50 lb-ft).

5. Reconnect Battery and Clear Codes

• Reconnect the battery terminals securely and clear the P0420 code using the OBD-II scanner.