Scanguage

As long as my fuel gauge works I can tell within a litre or so how much I have used and don't try to use my scangauge to calculate fuel, Just another thing to be bothered with at filling time. Waste of time.
BUT
I use a scangauge to indicate water temp and actual road speed and other functions.
On some autos the fluid temp can be shown which is an advantage to ID or prevent transmission overheating by taking appropriate actions. Saves cooking both the auto and engine.
ALSO
the scangauge can be used by someone else, or your self, to identify the area where a problems lies. as long as you carry a list of codes with you appropriate to the vehicle. Investigation may reveal it is a simple fix and your trip not ruined.
Even if you cannot rectify the fault, a passerby may be proficient enough to make a diagnosis using the scanned codes.You may be able to ID it yourself, ie, split turbo hose or similar fault.
For the cost of the device, if it saves you, just once, from from needing costly towing or roadside help it is good.
As well as that, if you scan codes before having a service, you know to a fairly accurate degree if the repair/service agent is reasonably honest or corrupt and greedy by stating untrue claims for additonal work or faults which don't exist.
All pretty obvious really.

Scangauge only has a very basic capability for code reading - is really a secondary function to fuel and engine management.

If you are not in interested in its main functionally and want a code reader I would look for something more suited.

Hi Ross, I use Scangauge on my 200 series cruiser to monitor Average fuel consumption, Current fuel consumption, Manifold pressure and Transmission temperature. Most of our driving in the 200 is towing and these four parameters are very helpful monitoring what is happening with the mechanics, particularly transmission temperature.

You can see error codes but you need the list of codes and their meaning to really make sense of them. The Scanguage manual list some of the common ones.

I have a Scangauge II in my Pajero. I bought it mainly to monitor the turbo boost (on a long hill, I didn't want to be melting pistons etc). I monitor coolant temperature and boost. These are the important items fro me. The other 2 items I monitor are Voltage and Inlet Air Temperature. If I had an automatic transmission, I would certainly monitor the fluid temperature.

You can buy an Ultragauge, which I think is a better unit - it can display up to 8 parameters, and it also has an alarm function (missing in the Scangauge). The only problem wit hthe Ultraguage is that you have to buy it in the USA, whereas you can get a Scangauge locally.

Our scangauge saved us last year as we were able to reset a fault code on the turbo intercooler blockage on our challenger when we were half way between Innaminka and Arrabury.We were in limp mode every 5-10km and then i would reset the code and continue. Without gauge would have been a costly tow recovery being 100's of kilometres from anywhere. I was also able to fault the turbo hose leak when able to check boost and see that we were nowhere hear 15-18lbs only pushing 5-7lbs boost when under boost. I have had ours for 3 cars now and would not be without it. Just being able to see what are normal engine parameters so when things go wrong you are able to pinpoint the issue in the middle of the desert.

Though it can provide info on a good number of techno-parameters, I bought mine purely to confirm transmission fluid temperature at any time (200 series TD, towing an offroad van). On the face of it, transmission fluid shouldn't get hotter than the engine coolant I suppose, but then, it probably does at times...better to know what IS actually going on in there, than to be 'in the dark' I say :-).

Ross,
Some say you can't reset codes with the scangauge 2 to get you mobile when you really have to but you can.

Note the code address and turn off the engine, turn the ignition on without starting the engine and then clear codes. You can normally download different manufacturer codes, I know my vehicle has 1300 codes all up.

It is very handy for drive train and engine monitoring.

Over the last 5 years, my stock standard 200series has thrown a code - one was an EGR code and the other was when crawling on low range. Both times cleared the codes with scangauge and never saw them again.
Can google the codes to get a list of what they mean, or check the workshop manual.