how to fix P0420 code on Cadillac Escalade T1XX (2021-Present)

Symptoms

• Check engine light illuminated
• Decreased fuel efficiency
• Rough engine idle
• Failed emissions test
• Unusual exhaust smells (sulfur or rotten egg odor)

Diagnostic Steps

1. Scan for error codes using an OBD-II scanner to confirm P0420 and any related codes.
2. Inspect the exhaust system for leaks and damage, particularly around the catalytic converter.
3. Check the oxygen sensors (pre-catalytic and post-catalytic) for proper operation and functionality.
4. Measure the voltage output from both the upstream and downstream oxygen sensors.
5. Test the catalytic converter for blockages or physical damage using a backpressure test or temperature differential method.
6. Review fuel trim data to identify any potential fuel delivery issues.

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to avoid electrical issues while working on the vehicle.
• Raise the vehicle using a jack and secure it with jack stands.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Use an O2 sensor socket to remove the sensors from the exhaust system.
  4. Install new O2 sensors by reversing the removal process; ensure they are adequately torqued (typically around 30 lb-ft).
  5. Reconnect the electrical connectors to both sensors.

3. Inspect and Replace Catalytic Converter

• Sub-steps:
  1. Remove any components obstructing access to the catalytic converter (e.g., heat shields or exhaust pipes).
  2. Unbolt the catalytic converter from the exhaust system using a socket wrench.
  3. Inspect the old catalytic converter for signs of damage or blockage.
  4. Install the new catalytic converter and torque bolts to the manufacturer's specifications (usually around 30 lb-ft).
  5. Reattach any previously removed components.

4. Reset the Engine Control Module (ECM)

• Sub-steps:
  1. Reconnect the battery.
  2. Use an OBD-II scanner to clear the P0420 code from the ECM.
  3. Start the engine and allow it to reach operating temperature.