erratic guages/failed smog on 2005 Ford Mustang

I have an issue as my 2005 mustang. It failed smog today with the PO4063 error. I have had a check engine light on for a couple of months, the fuel guage and the speedometer guage are both erratic and not accurate. I am taking it in to a mechanic as I need my car, but am really concerned about getting screwed as I have never failed an emissions test and do not know much about them.

Any ideas what could be wrong or what is required to correct?

Thank you!

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This is pretty common on the 2005 Mustangs, it's caused by failing stepper motors in the instrument cluster, they control the movement of the gauges. There's a guide on how to fix them here - www.2005-mustang-speedometer-problem.com