97 BMW 740IL 4.4L V8 - Fault Codes P0420 and P1384: Oxygen Sensor or Knock Sensor Issue?
Diagnostic scan shows two fault codes on a 1997 BMW 740IL with a 4.4L V8 engine: P0420 (Catalyst System Efficiency Below Threshold - Bank One) and P1384 (Knock Sensor 3 Circuit). Is this issue primarily related to the oxygen sensor, or could it be caused by another component in the exhaust or engine system? Any insights or troubleshooting steps would be greatly appreciated.
O2 sensors are unlikely to be the root cause here. The P0420 code strongly suggests a failing catalytic converter in Bank One, especially given that this vehicle is over 12 years old. It's important to install a high-quality catalytic converter—performance and longevity vary significantly by brand and quality. Poorly made units may need frequent replacement. After replacing the catalytic converter and clearing the codes, monitor whether P0420 returns. If it does, investigate wiring connections or grounding issues related to the knock sensor 3 circuit as well. Don't overlook the physical condition of the sensor itself. Good luck with your repair—please update us on the outcome.