Another Nav Problem

[spike147]

Hi Guys,

It's another nav problem I'm afraid, I've recently upgraded my MKIII sat nav to MKIV from Bimmernav. With the MKIII I used to get an intermittent problem where the sat nav wasn't quite lined up with the car, ie. it would show me about 50 metres to one side of where I was. Then it would constantly try and 'snap' to the street it thought I was in, and then snap again when it realised it was wrong.

If I input my position manually by using the junction of two roads it would fix it for a couple of days, and then it would lose it again.

The thing is I've started getting it with my MKIV which suggests something like an antenna problem to me. It's just strange that it almost knows where I am, but not quite.

Sorry for the long message, if anyone can help I'd really appreciate it.

Simon.

[RichardP1]

When not in guidance mode (i.e. no route planned) does the symbol for the satellite in the top right corner of the map have any dots around it? If not then there are no satellites being picked up and the Nav is using the wheel sensors to measure it's position using dead reckoning. Id guess that the reception is intermittent, possibly a faulty wire, otherwise it would not have picked up your new location when you installed the Mk IV.

If there are regularly no satellites when the car has been in the open for at least 15 minutes, then the easiest way to check the GPS antenna is to get a cheap one off e-bay with an SMB connector, something like this http://cgi.ebay.co.uk/GPS-Antenna-amplifer-SMB-M-Magellan-Trimble-Lowrance_W0QQitemZ250052420941QQihZ015QQcategoryZ4 668QQtcZphotoQQcmdZViewItem connect it up to the back of the Nav and see if it makes any difference while the car is parked in the open.

You can also check the GPS receiver state from the hidden settings menu (Settings menu and press and hold the menu button for 10 seconds).

[trapdoor]

Sounds more like the wheel sensor input is not working correctly.

Go into the 'hidden' service screen for the nav (at work ATM so cannpt recall the key sequence) and whilst driving check the wheel sensor field increases/decreases with changes in speed. If it reads 0 all the time then the wheel sensor input is either U/S or you have a mis-wired loom (some were like that from the factory).

Nav inaccuracies of up to 100 meters nearly always indicate a Gyro or Wheel Sensor issue. If you were getting gross errors and no GPS displayed in the top RH corner of the map then I would suspect antenna.

See http://www.xoutpost.com/articles/all-...formation.html for more info on the problem, and the remedy. The article underplays the improvement in accuracy somewhat. There was a marked improvement when mine was fixed. And it isn't just X5's, mine was an E46. Go check the readings and the wiring,particularly if yours was a retrofit but factory fit nav's were also affected (but not in such great numbers).

[spike147]

Cheers guys, I'll double check your suggestions and report back. Now that you mention it, I don't think I've had the problem when I'm planning a route (I just tend to put the maps on when I'm driving around cos it looks cool!). I just thought I'd been lucky it hadn't occurred when I was planning a route.

It is a factory fit nav (and it's an E46 - am I still allowed on the forum? )

Thanks again.

Simon.

[spike147]

Hi,

I've just checked and it does appear that the wheel sensors are working OK, I get values are ound the 200 mark when driving around town, and when I stopped it returned to 0. Also I think I'm getting the dots (Very small white dots on the GPS symbol - is that right?).

Cheers,

Simon.

[KiwiJochen]

Check your DOP (dilution of precision) values in the GPS screen in the service menu.
The lower the DOP, the better. HDOP=horizontal, PDOP=postional
Typical good values are <2. A good car will show anything from 1.0 to around 5, subject to your current GPS constellation.
Often I will see 1.3 or 1.6, which is pretty good.

Greater than 5 is getting poor

Also, check your signal strength (S/N), typical is to have 2 or 3 atellites at around 10 to 12. Best i've ever seen is 20. More = stronger signal.
You'll generally receive 7 to 8 satellites.

A bad antenna will show around 2-3 S/N, and have more than 1 satellite with no signal

Jochen

[spike147]

Thanks Jochen,

The values I found were:
PDOP : 2.4
HDOP : 1.5
VDOP : 1.9

I seem to fairly consistently have 8 satellites visible.

I've attached photos in case there's any more info you can get from them.

Thanks again.

Simon.

[KiwiJochen]

Your GPS signal strengths and DOP values are all perfectly normal.

Are you sure the GPS is calibrated? You do need to go for a reasonable drive of around at least 10min at good constant motorway speeds (60mph) with steady GPS signal for the nav to properly calibrate the wheel sensors to the GPS speed.

When I fitted a Mk4 once I drove for 2 weeks without hitting 60mph and my nav took ages to calibrate - had me on wrong streets sometimes. Once calibrated, it was fine.

Jochen

[spike147]

Jochen,

Thanks again for your reply.

The car has certainly had the use you suggested to calibrate the sensors, that being said it hasn't been a problem for a good few days now so maybe it's sorted (fingers crossed).

It just seems strange that it does exactly the same as the MKIII before it did.

Thanks for your help.

Simon.