What Causes BMW Exhaust Catalyst Converter 2 Failure?

[DelAlexander]

BMW exhaust catalyst converter 2 failure is caused by oxygen sensor issues. 1. Introduction to the three-way catalytic converter: Installed as the most crucial external purification device in the vehicle's exhaust system, it converts harmful gases such as CO, HC, and NOx emitted from the vehicle's exhaust into harmless carbon dioxide, water, and nitrogen through oxidation and reduction reactions. 2. Principle: When high-temperature exhaust gases pass through the purification device, the purifying agents in the three-way catalytic converter enhance the activity of CO, HC, and NOx gases, promoting specific oxidation-reduction chemical reactions. CO oxidizes at high temperatures into colorless, non-toxic carbon dioxide gas; HC compounds oxidize into water (H2O) and carbon dioxide at high temperatures; and NOx reduces into nitrogen and oxygen. These three harmful gases are transformed into harmless gases, thereby purifying the vehicle's exhaust.

[ZaneLynn]

Last time my BMW had this warning light on, it turned out to be caused by long-term use of cheap gas from small stations. The poor-quality fuel didn't burn completely and clogged up the catalytic converter, making it hard for exhaust to flow. The mechanic showed me after taking it apart - the converter surface was covered in black carbon deposits, looking like burnt honeycomb briquettes. Now I strictly use 98-octane fuel and make sure to take highway drives every 20,000 km to clear carbon buildup, and the problem hasn't recurred. I suggest checking the oxygen sensor data stream when inspecting fuel quality - it's the first to alert when fuel quality is poor.

[VonCayden]

I encountered this issue particularly during cold starts in winter, with white smoke coming from the exhaust pipe accompanied by a sour smell. The 4S shop used an endoscope to inspect and said the ceramic substrate was shattered, though the metal casing remained intact. The technical director mentioned that in this generation of BMWs, the catalytic converter is positioned too close to the turbocharger, and continuous mountain driving causing overheating leads to thermal expansion and contraction, resulting in cracks. They replaced it under warranty with an improved version of the catalytic converter and also flashed a program to reduce exhaust temperatures. Later, I discovered in the car owners' group that many vehicles of the same model share this common issue. Now, during summer long-distance drives, I pay extra attention to the coolant temperature gauge.

[CalvinMarie]

Last time my car showed this fault code, and the data reading revealed that the voltage values of the front and rear oxygen sensors were completely synchronized, clearly indicating a failed catalytic converter. The original BMW catalytic converter was quoted at 17,000, which was really painful. Later research found that the exhaust valve was leaking engine oil, and the oil vapor entered the exhaust pipe, burning into carbon deposits that blocked the honeycomb channels. First, I spent 800 to replace the exhaust valve, then soaked and cleaned the catalytic converter with oxalic acid, and after reinstalling it, the fault light went off by itself. A reminder to everyone: before diagnosing this fault, check if the engine oil consumption has abnormally increased.