Here is the FAQ from the Ample Outdoors site (referenced by Scangauge):
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I need to monitor automatic transmission temperature, can the Scangauge II do this?
Yes, BUT.... it involes programming in an X-Gauge to suit your vehicle. Not all models are supported. We have developed a TFT X-Gauge for Holden vehicles (tested on the Jackaroo) and we are working on gauges for Ford (F250) and Toyota (Prado 120 and LC200) but it is not known when these will be ready. There are TFT X-Gauges listed in the X-Gauge commands list here, but these relate to vehicles in the American market and may not work on Australian vehicles.
At this time the programming sequence required for the Nissan D40 is not readily available. As was suggested trawling the net yields various things to try but none work.
If anyone else has cracked this problem please let me and the queue of others wanting this solution in on the secret! in the mean time Wholesale Automatic Transmissions in Melbourne can provide an AT Temp gauge kit for the D40 Auto circa $250