how to fix the 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

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

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors (typically near the exhaust manifold and after the catalytic converter).
  2. Disconnect the electrical connectors from both sensors.
  3. Use an O2 sensor socket to remove and replace any faulty sensors.
  4. Reconnect the electrical connectors securely.

Tools Required:

• OBD-II scanner
• Oxygen sensor socket
• Ratchet and socket set

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

• Sub-steps:
  1. Remove any heat shields or brackets securing the catalytic converter.
  2. Unbolt the catalytic converter from the exhaust system using a socket set.
  3. Inspect the catalytic converter for signs of clogging or damage.
  4. Install the new catalytic converter, ensuring proper alignment with the exhaust system.
  5. Tighten all bolts to the manufacturer's torque specifications (usually around 30-40 ft-lbs).

Tools Required:

• Socket set
• Torque wrench
• Cut-off tool (if the converter is welded)

4. Clear the Error Code

• Sub-steps:
  1. Reconnect the vehicle battery.
  2. Use the OBD-II scanner to clear the P0420 code from the engine control module.

Tools Required:

• OBD-II scanner