The DPF equipped 425 C9 Cat engines have a history of turbo failures. There are several of these coaches that have had 3 or 4 turbo failures. The issue is probably rooted in the necessity of having to use a variable geometry turbo as an exhaust brake.
The early production 425 C9 turbo chargers, which yours may have been one, had a very high failure rate. However, I have heard reports that the latter production turbo has a higher reliability, but I have not seen any reports that substantiate this.
Gerald
