Is the o/e sat nav/gps unit on a 2017 xj capable of displaying the vehicle speed?

 

Hi, indeed all GPS receivers can calculate the speed and direction from NMEA datastream, but in most cases (in fact any?) vehicle inbuild navication systems wont show you calculated speed, sine it will be different than your speedometer.
Speedometers are set to show you some % hihger speed than you are actually moving for several reasons (including road legistlation). Note that in certain conditions the GPS can also indicate slightly different speed that your vehicle are actually moving along the road. Modern vehicles, where the speedometer are electric there are possibility to adjust the %. Either by tyre circulation correction or actually speedometer %.

 

Good question and I don't know if that's possible on the X351 XJ?

I could do that with my old 2005 S-Type R. In the navigation settings you could monitor GPS speed. I only used it when trying to find the top speed on that car. One thing I did notice is that once you were in the 130-150 mph range I would see the GPS "gap" or jump as it could not keep up with the vehicle at those speeds.

Here is a thread on doing that on the S-Type. As I posted in that thread I was surprised at how close the GPS reading was to my speedo.
GPS Speed

Here is an old thread on how to get into Engineering mode on that car.
Engineering Mode

Attached is the TSB mentioned in that thread for background.
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