IIS - Create a Tracing Rule for Failed Requests

If a request to a server fails or takes too long, you can define a failed request tracing rule that will capture trace events for that request and log these trace events, as they occur, without having to reproduce the error. Events are written to the trace log only if the request exceeds the time interval allocated for the request to complete processing, or if the specified HTTP status and sub status code combination is generated for the response. The trace log only contains information specific to that failed request. You no longer must look through large log files that contain every request to find the information that you need about a specific failed request.

To create a tracing rule for failed requests please refer to this Microsoft Link https://technet.microsoft.com/en-us/library/cc725948(v=ws.10).aspx

In addition you can refer this article to enable site-level trace logging for failed request you can refer to this article IIS - Enable Trace Logging for Failed Requests.