COMAND inaccurate?

[NeilB]

I've had my '03 C220 (my first MB) for a few days and have noticed that COMAND is not giving accurate positions. Sitting on my driveway, it tells me I'm on the next road down (400 yards away) while on motorways, for example, it lags behind my actual position by about the same distance.

Is this a 'feature' or do I need to reinitialise COMAND somehow so it can reacquire the satellites?

Thanks in advance

NeilB

 

[Shude]

When I first fired my comand up it was a little confused, it thought it was a few miles away at the garage where I last had it powered up. After a few seconds it was fine.

Please remember that your driveway isn't actually a public road and won't be listed on the comand map disc, so it might get confused and say "off road" or something. Once or twice mine thought that I was on a road parallel to the one I was actually on, but it figured it out for itself after a few seconds and was back on track.

 

[saorbust]

Also remember that COMAND uses differential GPS to increase the level of accuracy - and this is only valid when you are moving. The source data may be invalid - check your NAV CD date. You might also wish to get MB to check out the calibration of the COMAND system as it may be faulty and require a reset.

 

[gerrym]

Comman problems

Hi, I have just got rid of a 211 E-class as it was having lots of electrical problems including the SatNav showing I was always somewhere different to where I was actually located.
I have spoken to the dealer since and he said it is a common problem, but easily cured with a reset
I would suggest you pay a visit to your local dealer.

On Shude's point, it does not matter what type of road you are on as GPS does not 'know' about roads, so it if functioning correctly, it will always show your correct position.


Cheers


Gerry

 

[sjmaxwell]

Another thought, I believe Comand is acurate to a certain tolerance, not sure what it is but it does mean it can be 'out' by a few meters!!

 

[guydewdney]

can the command bring up sattelite info? on my streetpilot I can get a page that has little bar graphs of the strength of all the sattelites it sees - when i'm in london or under lots of trees, the graphs go down until it gives up - or goes to 2D navigation. It also tells me the current accuracy - often I get it down to 6 or so feet - but more often its like 20 feet.

is your drive leafy? lots of tall buildings?

 

[mapleleaf]

There is a facility to calibrate the comand which you can do yourself . It wont break anything .

From the Nav menu at the bottom select settings

you should see two other options

Location
Calibration

Select location an tell comand where you are then it asks for a junction.

Select one from the list and tell comand how far away from the junction you are. If both roads are fairly well established you should get a confirmation that the location is accepted. If not , drive to a side road that is off a main A or B road and try again.

The calibration option lets you put in your tyre size. You also have New & used options. You wil get a warning that incorrect settings will affect comands accuracy

Once you have done these 2 things (its what a dealer would do anyway) Comand should know exactly where you are and how far you have travelled from A to B

If you need to reset Comand there is a hidden menu found by holding Mute & keys 1 & 3 all together for a few seconds (need to be in radio mode first for this to work) under diagnosis you can select a system reset. It basically reboots comands computer. This sometimes needs doing to kickstart a new phone install.

 

[clegsr]

You could also try another couple of things

If you press the "inf" button and go to position map it should show you how many sats it can pick up - 7 or 8 and you should get a good position fix- It may be that your house/drive is in a bad spot/trees etc.

But it also may be your dead-reckoning which is out:

Firstly check the front tyre sizes which will be something like:
235/65/ ZR 18 or something

Then go through the NAVI - Settings - calibration - it will give you a warning but dont worry you can Cancel out of it without changing anything.

The screen should show the tyre size as 235 / 65 18 but it may just show:

000 / 00 00

in which case it hasn't been set for your car - or it may show other numbers if the tyres have been changed.


If the numbers are different from the actual tyres you have then the COMAND will get confused as you drive about as to where you actually are.

 

[MBenzNL]

Even with the calibration way off - comand is self learning meaning that if the speedpulse is way off (like let's say when comand is installed in a W201 in which it only gets 1/6th of the number of speedpulses) it will adapt by itself...

When a 463 G-class comand is inatlled in a W203, people tend to get the same inacurate problems due to a gyroscope that is 10 degrees off (15 instead of 25 degrees)...I presume you have your comand installed from factory and still have some warranty on it - let the dealer handle the problem.

greetingz,

 

[NeilB]

Thanks for the suggestions, guys. The car's going in to the stealer next week to have a 6310 cradle fitted, so I'll ask them to check COMAND.

I've enjoyed my first couple of weeks of MB ownership - I just wish I could trace the annoying whistling whirr that's coming from the centre console area. At first, I thought this was the nav CD spinning but it happens with the CD out. Could it be the COMAND gyro or is it likely to be something within the climate control system?

Oh, I got a slow puncture too but I can't blame the car for that!

Cheers

Neil

 

[mapleleaf]

Thanks for the suggestions, guys. The car's going in to the stealer next week to have a 6310 cradle fitted, so I'll ask them to check COMAND.

we could have helped you fit that cradle . is the car prewired for phone ? if so I have the cradle available ,(about £150 brand new) it just plugs in to the prewiring in the centre armrest. 2 minute job.

Comnd has a fan that is always whirring whilst the ignition is on. but it shouldnt be intrusive.

 

[NeilB]

Thanks for the offer Steve. However, I got the dealer to agree to provide and fit the cradle free-of-charge when I bought the car.

Regarding the fan, presumably this isn't running when the Comand unit is switched off, or is it always running when ignition is on?

 

[Flyer]

Regarding the fan, presumably this isn't running when the Comand unit is switched off, or is it always running when ignition is on?

It runs on until the temp in COMAND has reduced sufficiently, ignition on or not. If COMAND has been on for a couple of hours, with say, Nav and music on, it can take 20 minutes or so to cool down enough for the fan to go off. COMAND does monitor your battery though, so there's no danger of it flattening it.

Cheers
Andrew

 

[NeilB]

Thanks Andrew

I'll try turning COMAND off, leave it for half an hour,and see if it still happens. I'm beginning to think though it's something in the climate control - when I turn it off (i.e. decrease the fan speed until the display reads '0'), it stops.

I'll start a thread in the Interior section and see anyone else has come across this.

Cheers

Neil

 

[Maff]

I had the same problem with COMAND 'jumping', and sometimes being 400 yards out of sync.

The problem - faulty gyro AND the speed pulse (tells comand how fast your traveling) had disconnected itself through a loose connection.

Hope this helps,

Matt.

 

[MannfredTMann]

Question on Calibration

I recently ordered a Comand 2.0 from SteveNL and had my steeler install - they were keen as they had never installed an aftermarket comand before. Using over last few days I have noticed that the calibration seems off - i.e. position relative to map is out of about -50m from current position and when you stop it still catches up or adjusts.

Is there any way I can check to ensure the steeler connected the speed pulse correctly without removing the unit to check? Is there anything else they could have missed that could cause this?

Cheers in advance

 

[prprandall51]

Navigation system technology

Regarding some of the posts on this thread, here is a quick background on how Nav systems work (thought it might help clear up some mysteries).

There are three positioning technologies inside a Nav system:
Gyroscope (so the vehicle knows which direction it is pointing)
Wheel sensor (so the vehicle knows how fast it is travelling and how far it has travelled)
GPS (so the vehicle knows it's absolute location and - only possible when moving - it's direction of travel, speed and distance covered).

Can't speak about the latest systems but certainly until recently, GPS was not necessarily the most important sensor (indeed, early nav systems worked before GPS became publicly available). This must still be true to an extent because the vehicle never "loses" itself even after passing through tunnels or when travelling around cities with lots of high-rise buildings (where you get what is known as the "canyon effect" in which the GPS receiver can no longer see enough satellites to compute a position). Furthermore, until 2000, GPS signals were deliberately skewed by the American govt using a system called SA (Selective accuracy, I think) so that the position could never be guaranteed to be accurate to more than 100m - and that's not very accurate. If your nav system software was designed before 2000 it just won't be paying much attention to the GPS signal, it will assume that the postion data is simply not very accurate. GPS will be used for initial fixing and periodic realignement (and, of course, accurate speed and direction data, which were largely unaffected by SA).

With this background (GPS deliberately made innacurate, high-rise buildings, tunnels, etc) two key technologies were developed that made Nav systems possible - and those technologies are still used today. The first is map matching. With this, the nav system is constantly collecting a profile of the road from the sensors and comparing it to the map data. For example, if you just drove through a 130 degree left bend, went 125 metres and then through a 45 degree right bend then you must be ... there .. because that's the only place on this road where those two bends occur in that geometric layout. Map matching is always re-aligning the nav system to your exact location by comparing sensor signals with the map data. If you have the incorrect tyre size entered in the nav system, then I could imagine that map matching would quickly break down leading to innacuracies.

The scond technology is very simple but very neat, it is called route snapping and all it does is say "Wherever you are, you have to be on a road if you are moving any distance". That is why you will see posts that say "my system thinks I am in the adjacent road" or "my nav system is about 300m behind my actual location on the road" but rarely "my system thinks I am in my back garden" or "my system shows me ploughing through the adjacent field". Of course, nav systems also recognise the concept of "off-road" but once you start moving any distance and at any speed, it assumes you are on a road and looks on the map for one that is most likely. It only shows "off-road" when there are no candidate roads that fit the vehicle's position. I expect that nav manufacturers rely much more on GPS than they used to to resolve vehicle positioning now that GPS is accurate to around 5 metres or even less.

Two other notes: The gyroscope is critical and one reason is because it is this that allows the system to tell you exactly which exit to take on the roundabout using the "Take the next exit" message - only possible because it knows the exact direction your vehicle is pointing. Blaupunkt systems used to (still?) do this brilliantly. My Becker system waits till I am already off the roundabout and heading down the road before it tells me to leave the roundabout with a confusing "Turn left now" instruction...

Secondly, sorry to contradict a previous post, but nav systems don't use differential GPS. Differential GPS is a combination of a GPS signal and a radio signal (typically broadcast on RDS) that allows the inherent innacuracies in GPS to be calculated out leaving you with a super-accurate position fix - down to a few centimetres on some systems. Before the US govt switched off SA in 2000 and allowed all GPS receivers to instantly achieve 5m or less accuracy, differential GPS was the only way of getting an accurate position. It is widely used for field surveying - and indeed is the technology that allows the map data to be so accurate. Accurate enough for the next great thing: Curevtronic. The ability for the car to swivel the headlights into approaching corners using the map data rather than the steering wheel postion, speed and yaw-sensor data. Whether this works remains to be seen....

Philip