Is This 3rd Replacement NAVI Unit Working Properly?

When I start the car in the morning & press MAP, I get the map screen with no satelite showing, no coordinates showing & no streets... Mostly a grey screen.

Within moments everything "clicks into place" & everything is there showing 5 satellites. As I drive off the driveway, I pick up 1 or 2 more satellites.

On all the old units, as soon as the screen came on whether by pressing MAP, or the system booting up after starting the car, there were 6-7 satellites & all the streets & coodinates were visible immediately. (although the direction of the roads might have been displayed in a random wrong angle until I backed off the driveway).

 

And why did you replace a good working unit?

 

Dude... be real. would a Dealer replace working units? Twice? They failed & either made the whole Comand go dead, or displayed "Navigation Not Available" on the screen.

The operation I described is how they worked when they used to work.

 

I am not a Mercedes nav expert but I do know GPS and how it works. I cannot tell you if your new unit is working right or not but maybe I can give a little insight into how a GPS receiver works. No GPS receiver can immediately come on with the right location and tracking 6 or 7 satellites unless the unit has been powered continuously.

But there may be explanation of what your old GPS receivers were doing. When you turn off most GPS receivers, the location is stored in non-volatile memory. When you started with your old GPS units, they probably displayed this old information and then updated when real GPS reception was attained. I would guess this is what was happening with the old units since you did say it updated after you backed out of the driveway.

Not sure about the new one but I would guess that it has a slightly different software that does not display this information. Since you really have to wait until you really are tracking the satellites to get useful information, it would not hurt your navigation anyway. But that is a guess only.

So why does a GPS receiver store the last location? Without going into a lot of technical detail, it is so the receiver can acquire the satellites as quickly as possible rather than have to start over from scratch. In most receivers, it cuts the satellite acquisition time from minutes to tens of seconds. That is a real advantage with GPS receivers in the dash of a car because, unlike handheld units, they are almost always in the same location as when they were turned off and the acquisition time is minimal. Of course, I can put my handheld GPS receiver in a rental car a lot easier than your dash mounted receiver. Everything has its advantages and disadvantages.

Not really an definite answer to your question but maybe it will help you understand what might be happening.

 

Perfect! That explains why when the unit was installed in the car, I had to ride around for what seemed a real while for the unit to display where I was... At first it was miles off.

 

Thanks for the explanantion pfphipps.

Sounds normal to me as well. When I park mine in a parking garage in the city, once outside, it takes a moment to orientate itself again, especially with tall buildings around. I've noticed this as well with the clock, when we change to daylight savings time and vice versa.

 

Back to the shop again. I can't beelieve that they all are just failing... something MUST be killing them. The display screen just says "Navigation Unit Not Available"

 

http://image1.maplink.com/images/gga/gga_nass_pat_c.jpg

But serially. Is the nav unit the only thing that's failing, or is anything else electronic failing at the same time?

 

Oh, I have the "usual" electronic gremlins, and also additionally I get a screen telling me that the Satellite radio is "updating stations" on the head unit, but not on the MFD, as the unit plays music... (I know there is a bulletin about this & how to fix it, but it never does it while at the dealer)

...but no, everything else about the audio/Comand works like its supposed to. I just get into the car, press MAP to see if its still working & it says "Navigation Not Available"

I'm really pretty calm about it all, but this is not going to make me a repeat MB buyer until they start having their electronics designed by a Japanese company. I don't know if I'd buy another MB even though I love the mechanical/ride aspects of the car. It just seems to be overly complex AND substandard electronics system design.

 

Im not a GPS guru, but I think pfphipps has some good info (maybe he can help me out here if I'm wrong...).

As I understand it, a GPS receiver fixes it's position by determining it's distance from a number of satellites using a distance intersection calculation. For this discussion, each satellite transmits a time signal and satellite number identifier. The receiver determines it's distance from a satellite by the time difference between signal transmission and receipt. For this to work, the receiver and satellites have to be in the same time reference. The receiver determines this time reference by iterative comparisons of all the satellite time signals it's receiving. Once the time reference is established, you're fixed.

When turned on, the receiver uses it's last known position reference to search for the fix. But if a unit hasn't been on for some time in an area, or if it is transported to another part of the world and then turned on, it has to re-establish the time reference. This takes a while to achieve, as the receiver attempts to get a position fix using the last time / position reference for itself and the satellites. However, about every fifteen minutes each satellite also transmits a file that has the position of each satellite at specific times. Using this file, the receiver can tell where it is in relationship to the satellites it is tracking much quicker.

So, if the reciever doesn't have a recent map of where the satellites are, it takes a while to get fixed.

R

 

Not too bad on the description or as they say, "close enough for government work".

I will add one more confusion point. As opposed to most communications satellites, the GPS satellites are not stationary above a point on the earth but rotate around the earth. Therefore, they are moving objects but the satellite orbits are well known and do not change much. So if a receiver has seen the signals before, the receiver can predict the satellite position based on what it saw the last time. To speed acquisition, the receiver can use old data and use this transmitted satellite location data to tweak the satellite position later.

There is also another transmission from another satellite that gives last little bit of correction to a GPS location in the USA. 25 ground receivers around the country measure their GPS location and then compare it with where they know they are at. This gives a correction to the GPS signal that is transmitted to a satellite and then to ground. It is called WAAS (Wide Area Augmentation Service) and most receivers can use it now, even the cheap ones. I assume the Mercedes receiver uses it but I do not know. If it is using WAAS, it requires a little more time to acquire the accurate location.

Only thing is that Barry’s receivers do not seem to work at all so all this theory of operation does not help him very much! Seems like there is something causing the recievers to go belly up. Hope he finds it soon.

 

It sounds like your current system is working reasonably well since it only takes a few seconds (?) to locate a number of sats. If the nav unavailable persists I would have the dealer first replace your DVD/clean the drive and if that does not fix the problem, replace the DVD drive that reads the NAV disk, I'm not sure if the navigation system is built into the drive or is part of the COMAND system and simply activated by interfacing with the drive.

If the NAV disk is not readable, the navigation system is unusable. You can simulate your problem easy enough by ejecting the disk. I think you will see the same symptoms you described, screen saying that nav is unavailable.


Good luck! While the navigation system has a lot to be desired, it is certainly better than pulling out maps.

For example, it has Yuengling in the destinations but does not map the actual streets directly along the brewery. Imaging, a german car that can't find a brewery! I'm sending a letter to Dieter Z.

 

They replaced this Nav unit. They say they found the reason they were failing was due to my CD changer. Who the hell knows !?!