Tns Out Of Sync.

[binswood]

I've got the TNS 200 system in my '02 Avensis. Last year the unit was replaced by an insurance claim, and since then its got out of sync with reallity twice. It gives me turn instructions about 150mtrs after I've made the turn! For example, it says "Turning slightly left at the roundabout, take 3rd exit" about 150mtrs after I've taken the exit. I have discovered that telling it that I've changed the tyres fixes the problem, but I'm not convinced that its always going to work and reckon that I've got a faulty unit. Anyone else met or heard of this problem?

[rf76]

Try unplugging it totally at the cd-rom unit and leave it for 5 minutes. It'll probably reset itself but you'll have to set the language up when you reconnect it and power it back up.

[binswood]

Try unplugging it totally at the cd-rom unit and leave it for 5 minutes. It'll probably reset itself but you'll have to set the language up when you reconnect it and power it back up.

Is this a known problem then, and is unplugging it likely to fix it for good? Telling it the tyres have been changed fixes it for a couple of months, and its quite easy to do - certainly easier than unplugging, waiting 5 mins, replugging and resetting various parameters.

Do you know what causes it?

[Avensis53]

I don't think your unit is faulty, the sat nav system uses 4 ways to work out where you are - the satellites give a rough position, to the nearest 100 metres is all the US government will allow, a gyroscope which detects if you turn, your roadspeed, and a technique called 'map matching'.

Obviously, errors can creep in to all these inputs, resulting in turn instructions after you've passed a roundabout such as you've experienced.

The accuracy of the roadspeed signal depends on the overall circumference of the tyres so the unit tries to compensate for tyre wear over a period, but obviously no two tyres will wear at the same rate, so this is where some of the error will creep in.

Re-calibrating the unit will fix the problem, and should always be done if you swap or renew the front tyres.

[binswood]

...snip

The accuracy of the roadspeed signal depends on the overall circumference of the tyres so the unit tries to compensate for tyre wear over a period, but obviously no two tyres will wear at the same rate, so this is where some of the error will creep in.

Re-calibrating the unit will fix the problem, and should always be done if you swap or renew the front tyres.

This I understand, but in my case the unit was working fine in the morning. I drove for about 100 miles without using it, stopped for an hour or so and when I started using it again it was around 250mtrs out. The tyres hadn't been changed and there was no gradual error creeping in - it jumped in suddenly.

The first time it happened, at the end of June, was the same: I used it to get to a meeting and it was fine. Driving home after the meeting it was wrong.

[Trafficman]

Not sure I agree with the 100m accuracy clame. More like 5-10 thse days as the uS have switched of Selective Availability (SA Flag). If it really was a case of direction and distance then Tom Toms would not work particularly well. Would personally advocate the power down option!

[Iain l]

Not too sure why the sat nav needs road speed info from the wheels unless its used to guestimate distance travelled when there is a poor or no signal. GPS is very very accurate these days, way more accurate than 100 meters. And there are certainly NO gyroscopes, smoke or mirrors involved.

The accuracy increases as the GPS receiver locks onto more satellites.

If yours keeps losing sync and it is improved by doing the tyre recalibration bit I would suggest that the GPS unit is receiving a very poor or intermittant signal and has to rely on the road speed too often. I have the full colour system in my spirit which I have dismantled, the GPS unit is in the box under the passenger seat but there is a coax which goes off to an aerial which is I beleive in the dashboard area. If mine were doing what yours does I would check the arial was not damaged or obstructed then check the full length of the coax for damage and check the connector into the sat nav box. If no faults can be seen then it would probably stand to reason that the sat nav box was faulty. If you are unlucky a bad kink in the coax could cause a deteriation in the signal received.

Iain

[mcvpjd3]

I've got the TNS 200 system in my '02 Avensis. Last year the unit was replaced by an insurance claim, and since then its got out of sync with reallity twice. It gives me turn instructions about 150mtrs after I've made the turn! For example, it says "Turning slightly left at the roundabout, take 3rd exit" about 150mtrs after I've taken the exit. I have discovered that telling it that I've changed the tyres fixes the problem, but I'm not convinced that its always going to work and reckon that I've got a faulty unit. Anyone else met or heard of this problem?

How many Sats does your TNS lock on to?

[Rvall]

I did have TNS200 (I think it was called that at least, it was full 5" screen with CD-player behind the screen...) on my Corolla Verso -05 (which I now have sold).

I had the same problem with mine, loosing my position or driving in the wrong direction. It happend once or twice every month. Sometimes it found it's way back after 10-15 minutes and sometimes you had to turn it off and wait longer. When it was out of sync, I could be driving north but on the map I was going south and every 10 seconds I was jumping 50 meter north (still pointing south) and then based on the information from the wheels I drove south again until next jump.

But I don't think the problem is mainly in your car because I have a friend who have one of these handheld navigators and they also stop working short periods every now and then and they are totally relay on the GPS system for the position. Since this is a computerbased equipment (and we all know PC and Windows reliability...) this doesn't always work like they are supposed to.

My guess is that sometimes the GPS system flips out or you have other strong transmitters nearby, then your system doesn't work correctly.

I must also praise the integrated system in Toyota (my only experience) since it also gets information from the wheels how you turn the car.

We have a new built tunnelsystem, south of Stockholm, that is 4.5 km long. (http://www.vv.se/templates/page3wide____2974.aspx)

This didn't exist on the roadmaps in my navsystem so the system doesn't know the roads. Every time I drove into the tunnels it looses the GPS, but still it can map me through woods and buildings above me and keep track of where I am within 10 meters and I come out on almost correct position where they join the old roads.

[funkyg]

This didn't exist on the roadmaps in my navsystem so the system doesn't know the roads. Every time I drove into the tunnels it looses the GPS, but still it can map me through woods and buildings above me and keep track of where I am within 10 meters and I come out on almost correct position where they join the old roads.

TomTom tries to keep in touch with where you are a different way. When you lose satellite signal it extimates where you will be by using your last know speed, location and direction. It's normally pretty good when I go through tunnells it's pretty much spot on when I come out the other end. Obviously it's dependent on keeping the same average speed.

Funkyg

[binswood]

How many Sats does your TNS lock on to?

It varies a lot, depending on where I am. I'm certain that this problem has nothing to do with the number of sats.

When it first happened, in June this year, I had no idea how to fix it so I did nothing, hoping it would fix itself. It didn't. It stayed about 200mtrs out for about 2 months, until I got into a mess when I was told to turn right 200mtrs after the real turning. In desperation I checked every setting I thought could have some bearing on the problem; re-callibration after a tyre change seemed the most appropriate so I tried that, and it worked. It stayed OK until recently when it suddenly went wrong coming home from a short holiday. I stopped, re-callibrated by telling it I had changed the tyres, and its now working fine again. It was working fine until it went wrong, and it did it quite suddenly. One minute it was working, and the next it wasn't; and it stayed wrong until I re-callibrated.