It is more often the case than not that once the facts are known, the problem is clearly visible, and the solution almost obvious. The engineer's key skill is asking the right questions, and putting the right weighting on the data available.
These are the same basic skills as the expert witness in such cases, though the aim of the expert witness is to stop at the point where the facts, as well as consensus and individual opinion on what they mean is known.
In troubleshooting, what the client want to know is if it can be fixed, and if so how. I have never had an expert witness case in which these were the court's questions.