Seems to be peculiar to a number of our 73 plate Scanyars. As far as I’m aware no vehicles other than those are affected.
GNSS: global navigation satellite system
The latest tachos have satellite positioning systems in them, and I would guess that your trucks are not seeing any satellites.
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Bizarre, but entirely conceivable I imagine.
Exactly as frangers says problem with global positioning system, aka where the truck is when starting and ending shifts. Would think it would require defecting for such and VOR.
It reminds me of the early days of tracking lorries, when we had the Eul-tracks transponders (or whatever they were called) mounted on the roof. If you put a galvanized tin bucket over it, nobody knew where you were 
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The GNSS signal stores the vehicles position at the start and end of the shift and also after three hours accumulated driving, so if you lose the signal for any reason when the tachograph is trying to read it, for instance when going through a tunnel or when the vehicle is in the workshop or anywhere the signal cannot be picked up the error will be shown.
As far as I can see the error message data will only be stored in the tachograph if the signal is lost for 12 accumulated hours of driving.
Presumably pressing OK clears the error message ?
If so I’d just clear the message and crack on 
Yeah it clears it when I press ok. It tends to appear when I turn the ignition on or off.
My my, what modern stuff is this. 
A quick question for all you young people. If you have to park up not far from home and want a lift from a passing driver does it do any good to wave a tacho disc, or even for a few of us on here, a logsheet/book? 
Can’t remember the last time I saw anyone doing that.
With mobile phones may anyone just contact workmates who are likely to be passing?
There have been posts about drivers (and vehicles) being “rescued” or “recovered” when a delay causes an unplanned night out etc. I can’t remember that being “a thing” years ago.
Seems that now fewer do real long distance work, and more do trailer swop/relay type operations, and truck hop all the time.
I suppose it’s more to do with the old days of no bunks or night heaters in cabs, It was so easy to get a lift, the very first driver who passed, that is if it was feasible regarding next day starting times quite a few did it. It was called a ‘dodgy’ because NO money was claimed.
I remember parking at Knutsford one Friday and hitching home to Nottingham, mind you I knew there was somebody who was going there next morning
But if you had to, what would you waggle, a little plastic card, or whatever you have these days, and if you did, could you guarantee to be picked up by the first lorry driver that came along.?
Even 22 years ago here I did it once after being told to leave my wagon at Bordeaux and wait for a driver who had been told to collect me. I rang him and he was delayed so I said I would try my luck with the tacho disc. 1st wagon picked me up and took me half way almost to Perigueux, then within 2 minutes one of our own came along and took me right to the yard. 
Is that a new scania? Funnily enough I’ve had no end of issues with those tacho,s fitted to scanias / daf xg/xf displaying allsorts of messages , daf much worse , I never had any issues for the previous 20 yrs ( I’m guessing at 20 yrs , or when they came out ) using those tacho,s in scanias .
Forever leaving them at the vmu for technicians to look at , once on the road I had to divert into depot ,they said I was ok to continue but if my memory services me right they said it had to be sorted within 7 days.
Must admit they’ve been better of late but do get the odd message , other day I put my card in and it wouldn’t go past my name , wouldn’t eject card , had to take it to vmu to get card out , they said it’s a regular thing , as I say never had it before latest batch of scania / daf .
Yeah, 73 plate Scanny Ady.didnt worry me as all of our 73’s seem to do it.
Anothe day another message , seen it before though , daf but same tacho as moaster originally posted
@ady
There’s a difference between the mileage recorded by the GPS signal and the vehicles motion sensors.
It could happen where a GPS signal is interrupted such as in a tunnel or anywhere a GPS signal is week or none existent.
If it’s a regular error message and you cannot see an obvious reason for the GPS signal being interrupted get the garage to check the vehicle motions sensors.
I would expect it to be an issue if putting the vehicle on a train or using a ferry: as the vehicle moves but there is no input from the gearbox. The vehicle moves without the tacho registering anything and so suspicions would be raised.
In the case of losing signal the opposite is the case isn’t it?
The tacho “knows” the vehicle is moving because of a signal from the gearbox, but the GNSS does not see it. I would think that is not high on the list of possible fiddles to be worried about.
I leave it at the vmu when I get back tacho & let them deal with it , just WhatsApp a pic to office when it comes up to cover me .