Easiest way is Torque Pro and a Bluetooth OBD dongle. I've recently upgraded to a ScanTool OBDLink LX and their official OBDLink app. Normal SAE-standardized PIDs are in Mode 01, every OBDII car supports those. Mode 21/22/23 are what I suppose you could call OEM-specific PIDs. Usually you have to pay crazy amounts of money and enter contracts to get detailed information about what PIDs are available and how to correctly understand them, but it's not exactly rocket science.
I don't really have a place that explains how to use Mode 21. I've been poking around the CAN Bus for a while trying to see if I can spot interesting things (a whole other subject), and a lot of diesel truck owners and tuner crowds use the these modes to get specialized sensor readings, so I started searching for what support the Mirage has. I used the plugin mentioned earlier to find the supported PIDs. Literally all it does is read the PIDs one by one, and record which ones respond with data. It also supports alternate ECMs, like the TCM, ABS, SRS, etc. Reading undocumented PIDs is supposed to be completely harmless but there's always warnings that it could cause unexpected behavior, blah blah...
When you read a PID (let's say, Mode 21, PID 01), it'll return a packet of data in Hex, usually no more than 7 byte pairs (reference these as bytes A through G). Each Hex byte will always be between 00 and FF, which when converted to Decimal will be 0-255. In my notes above, byte B is Speed in KPH. So if you read PID 01 and the response is BA303CDC57, byte B here is "30", which 48KPH, or 29MPH. Some data is spread across two bytes, like Mode 01 PID 0C, which is Engine RPM. The formula for reading that response is "((256*A)+B)/4". Some PIDs are easy to decode, just by plotting them on a graph while the car is moving. The A/C Compressor one was real easy because it was a sawtooth pattern on a graph, and if you turned off the A/C it stuck low.
I'll update the top post with all the PIDs I found, and as I decode them I'll update the notes. In theory, you can take these PIDs and put them in any reader or app, be it Torque Pro, OBDLink, even ScanGauges will take custom PIDs (dunno if they can do modes other than 01 though).
I'll try to answer any questions that come up! I know enough to be dangerous ;P
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View my fuel log 2017 Mirage GT 1.2 automatic: 37.5 mpg (US) ... 15.9 km/L ... 6.3 L/100 km ... 45.0 mpg (Imp)