Hmmm...did you see this thread from over the weekend discussing this sensor's location?
Does the car have any driveability or shifting issues (assuming it's a CVT)?
I have an older (1999) Eclipse and have had the output speed sensor go bad a couple of times. This is a non-ABS car. When it happens, the speedometer doesn't work and the car will only limp along in 2nd gear. The sensor is nothing more than a magnetic pickup externally threaded into the transmission. It can be replaced by just popping the hood and screwing in a new one. It can be checked just by measuring its resistance. Not sure if this is the same thing in the Mirage. I didn't even bother taking the car in to have it done under warranty because the sensor wasn't expensive.
View my fuel log 2015 Mirage ES 1.2 manual: 51.4 mpg (US) ... 21.9 km/L ... 4.6 L/100 km ... 61.8 mpg (Imp)