how to fix P0420 code on 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 all tools and parts required for the repair.
• Disconnect the battery to ensure safety while working on the vehicle.

2. Oxygen Sensor Replacement

• Tools Required: O2 sensor socket, ratchet and extension, torque wrench.
• Remove the upstream oxygen sensor:
  • Locate the sensor on the exhaust manifold or just before the catalytic converter.
  • Use the O2 sensor socket to remove the sensor by turning it counter-clockwise.
• Install the new upstream oxygen sensor:
  • Apply anti-seize compound to the threads of the new sensor.
  • Thread the new sensor into place and tighten to manufacturer specifications (typically around 30-40 ft-lbs).

3. Catalytic Converter Inspection/Replacement

• Tools Required: Socket set, jack and jack stands, torque wrench.
• Inspect the catalytic converter for damage:
  • If damaged, proceed to replace.
• To replace the catalytic converter:
  • Raise the vehicle using a jack and secure with jack stands.
  • Remove the bolts securing the catalytic converter to the exhaust system using the socket set.
  • Detach any hangers or supports connected to the catalytic converter.
  • Install the new catalytic converter and secure it with bolts, tightening to the specified torque (usually around 30-45 ft-lbs).

4. Final Checks

• Reconnect the battery.
• Start the engine and allow it to warm up.
• Clear the P0420 code using the OBD-II scanner.