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

Learn how to diagnose and fix P0420 code in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts.
• Park the vehicle on a level surface and engage the parking brake.
• Disconnect the battery to ensure safety.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Instructions:
  1. Reconnect the battery and start the engine.
  2. Use the OBD-II scanner to monitor the live data of the oxygen sensors.
  3. Compare the readings from the upstream (pre-catalytic converter) and downstream (post-catalytic converter) sensors.
  4. If the downstream sensor shows minimal voltage variation compared to the upstream sensor, it may indicate a faulty catalytic converter or sensor.

3. Replace Faulty Oxygen Sensor (if necessary)

• Tools Required: Socket set, O2 sensor wrench
• Instructions:
  1. Disconnect the electrical connector of the faulty oxygen sensor.
  2. Use the O2 sensor wrench to remove the sensor from its mounting location.
  3. Install the new oxygen sensor and reconnect the electrical connector.
  4. Torque the sensor to the manufacturer's specifications (typically around 30 lb-ft).

4. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, cutting torch (if needed), exhaust clamps
• Instructions:
  1. Disconnect the exhaust pipes from the catalytic converter using the socket set.
  2. Remove any mounting brackets or bolts securing the catalytic converter.
  3. If the converter is damaged, install a new one by reversing the removal process.
  4. Ensure all connections are tight and secure.

5. Clear Codes and Test Drive

• Tools Required: OBD-II scanner
• Instructions:
  1. Use the OBD-II scanner to clear the P0420 code from the vehicle's ECU.
  2. Conduct a test drive to monitor the performance and ensure the check engine light does not reappear.