The EcoRoute
HD comes with an OBD2 dongle that sends the car's engine data via BlueTooth to the compatible Nüvi navigator device, so in theory the data should be just as accurate as with the ScanGauge.
It can also show and reset engine error codes.
Description:
Garmin ecoRoute? HD : Be your own mechanic - monitor your engine and save fuel
Here's a review:
Garmin ecoRoute HD Review & Rating | PCMag.com
Looks tempting.