how to check if the catalytic converter is bad on my BMW 5 Series G30/G31 (2017-2024)?

Solution

1. Preparation

• Tools Required: OBD-II scanner, pressure gauge, thermocouple, socket set, safety goggles, gloves.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts during the inspection.

2. Error Code Analysis

• Connect the OBD-II scanner to the vehicle's diagnostic port.
• Retrieve and record any error codes related to the catalytic converter (e.g., P0420).
• Clear the codes and take the vehicle for a test drive to see if they return.

3. Exhaust Back Pressure Test

• Locate the O2 sensor before the catalytic converter and remove it carefully.
• Insert the pressure gauge into the O2 sensor port.
• Start the engine and measure the back pressure at idle (should be below 1.5 psi).
• Rev the engine to 2,500 RPM and measure again (should be below 3.0 psi).
• If readings are above these values, the catalytic converter may be clogged.

4. Temperature Test

• Attach the thermocouple to a digital thermometer.
• Insert the probe into the exhaust before the catalytic converter (inlet).
• Measure the temperature at idle.
• Then measure the temperature at the outlet of the catalytic converter.
• A significant difference (more than 100°F) indicates inefficiency.

5. Oxygen Sensor Inspection

• Reinstall the O2 sensor after completing the pressure test.
• Use the OBD-II scanner to monitor the live data of the upstream and downstream O2 sensors.
• Check for proper voltage readings; the upstream sensor should fluctuate, while the downstream should be more stable.
• If the downstream sensor is not responding, it may indicate a failed catalytic converter.

6. Final Inspection

• Inspect the catalytic converter for physical signs of damage or melting.
• Replace any damaged components as necessary.