Prolonged rich running damaging the converter

A converter destroyed by running rich for a long period, which overheats it. The mechanism is worth understanding because it is not simply "too much fuel": unburnt fuel reaching the converter burns inside it, and the converter has no cooling. Temperatures climb far beyond design, and the substrate sinters, melts or breaks up.

So the converter is the last casualty of a fault that was reported earlier. A failed oxygen sensor, a leaking injector, high fuel pressure or a dead coolant temperature sensor holding the engine in warm-up enrichment will all do it — and each will have stored its own code first. A converter efficiency code arriving after weeks of an ignored rich condition is the sequence, which is why the earlier codes matter more than this one.

Replacing the converter without correcting the mixture destroys the replacement, often quickly. Confirm fuel trims are within range and the mixture controls correctly before the new part goes on, and be aware that a broken-up substrate can migrate downstream and restrict the exhaust, which produces a power loss that reads as a turbocharger fault.