Tracking

<div class='quotetop'>QUOTE(vmbosik @ Aug 2 2007, 04:23 PM) [snapback]489643[/snapback]</div>

This happens with all GPS derived road navigation systems. Although there are techniques which reduce the frequency of occurance, all systems will get off-track occasionally. Usually, all you need to do is wait a while, until the error becomes large enough to force the nav system to rethink its placement.

It can be a bit strange sometimes, like when the nav says you are going north and you know you are headed west into

 

Have you tried recalibrating the GPS? There should be a menu option where you point the car due north, go into calibration mode, then drive a tight 180 or 360 degree turn, then done. Works in my '03 build Mazda RX-8 that uses much older '02 nav technology.

 

<div class='quotetop'>QUOTE(vmbosik @ Aug 2 2007, 11:49 PM) [snapback]489774[/snapback]</div>

If the GPS is working you don't have to do this. What you are seeing is a loss of GPS data which forces the NAV system to dead reckon. The system then latches onto the nearest road. When a good GPS fix is obtained, the NAV system should automatically jump back to the correct position.

If your Lockpick is disrupting the speed input, then the dead reckoning is not going to work, and your position will stand still until another good GPS fix is obtained.

This leads to the next question: what is wrong with your GPS? If this is happening frequently and in multiple areas, then get it checked.

Tom

 

<div class='quotetop'>QUOTE(vmbosik @ Aug 3 2007, 11:52 AM) [snapback]489991[/snapback]</div>

Have you changed tires recently? If so, have you told the nav system to recalibrate to your new tires?

There is an option in the nav system to get it to calibrate to the tire size. This might just help it enough to track better.

 

Next time it gets off track, look at the upper left corner of the Nav display and see if the "GPS" indicator is there. If not, it is a GPS problem.

If the "GPS" indicator is there throughout the problem episode, then I would suspect the lockpick is disabling the speed sensor for too long a time. The GPS-only solution is not very accurate and you can get "lost" after a while in non-GPS mode, especially if the map-matching is poor.

You may be surprised to find out that the GPS on the car is only accurate to 100 feet or so at best. It appears to be more accurate because of the use of the speed sensor (wheel turn counter), the turn sensor (gyroscope) data, combined with map-matching which the Nav system uses to derive a "blended solution" to the location problem.

To see this blending in action, find a road where there are two parallel, slowly diverging paths, such as an exit ramp off a freeway that parallels the freeway for 1/4 mile or so. Drive on the freeway portion for a while to get located on it. The system assumes you are continuing on the freeway as you drive; so if you take the ramp, it will take a little while to figure out that you really are on the ramp, not the freeway; your position will then discretely jump to the ramp from the freeway.

This blending of location methods is why we need to separate them to diagnose your problem. Inaccuracy can be caused by failures in any of the Nav components.

 

<div class='quotetop'>QUOTE(KTPhil @ Aug 9 2007, 01:03 AM) [snapback]492860[/snapback]</div>

I can almost gaurantee that you are losing GPS signal.

I have the same problem in my prius, except my situation is a little different than yours. I have an 05 prius that came with no navigation and no jbl system. I then took the MFD and navigation unit out of another prius and put it in mine. There was some work to be done, but it started to work. I also did not have the antenna that comes with it. I wanted to purchase the original Toyota antenna, but they were asking something ridiculous like $400 for just the antenna. I instead purchased a Chrysler antenna for about $50 and modified it to work with the system. I loose signal every now and then and the map does get lost. I say there is nothing you can do about it unless you would like to bring it to a Toyota dealership and pay an nice person load of money to get the antenna replaced. If anyone has a good source for Toyota OEM gps antenna, then please let me know.

Thanks,
Kamil

 

I was driving my 2005 today, no LockPick, and after crossing a river on a ferry, I lost GPS and the NAV system got completely lost. It showed my driving across fields and crossing roads that weren't there. Turning off the car and then back on didn't help. I found my way home, ignoring the idiocy of the nav screen, and shut the car down for a half hour while I ate lunch. Later, I had to go to a store about 5 miles away. No nav on the way there, still driving across fields and going south while I was heading north. I was in the store maybe 20 minutes. When I came back out and started, I switched to the map and GPS came on instantly and the map centered on my location. GPS stayed on the rest of the way home. GPS was gone for perhaps 2 hours.

I'm going to report this to the dealer since I have 34K miles on it. If GPS is working, there's nothing for me to show them, but I want them to know there may be a problem before the 36K mile warranty is up.

 

My previous car was a 2006 Mazda 6, which also had a Denso Navi unit. When I first got the car I had the exact same problem as you're experiencing. I found my way into the hidden diag screens, and saw immediately that the GPS was not working at all. It turned out that some connectors had been left unplugged at the factory, though it took 3 trips to the dealer to convince them as to what was wrong. <_<

You don't need to wait for your navi to get 'lost' again to check the GPS. Go into the diagnostic screen (hold the 'Info' button & turn your parking lights on/off 3 times quickly.) Follow the menus to the GPS Info screen, and you should see something like this:

[attachmentid=10738]
It may take a few minutes to establish its position. The STS column for the satellites should go from a "-" to "T" to "P". Once you get 3 or 4, the status should change to 2D or 3D (2D indicates it doesn't have enough satellites to give it a 3D position, which is far more accurate.)

Driving my Mazda for a month without the GPS gave me a good view into how the system works. Its primary means of tracking is the dead-reckoning system, which is surprisingly accurate. It's how auto navigation systems worked before GPS was available. But as you've noticed, a big part of how it operates is to try and keep itself on the roads it 'knows' about. What it uses the GPS for is to periodically compare the GPS position to the dead-reckoning location, though it only does this at intervals. I've not been able to determine what that is, or if it's by miles or time.

There was a road I frequently travel where they changed a right-angle turn into a big, sweeping curve, though the navi system did not have the update. It was fun to watch the map as I drove through that, with the location arrow trying to keep on the road. It looked like it was skidding sideways, and when I got far enough into the turn, it would finally slide over to where the map had no road (but where I actually was.) When I got back onto the 'old' section of the road, it would show me on course, but the arrow would be 'crabbing' slightly (not pointed in my exact direction of travel.) After about 2 miles it would correct itself.

<div class='quotetop'>QUOTE(Bill Merchant @ Aug 13 2007, 02:24 AM) [snapback]494580[/snapback]</div>

This situation is actually mentioned in the navi manual in the appendix, under conditions that can cause the tracking to be off. It's surprising that it took so long for the GPS to correct itself, but that could be partly due to the fact that moving the GPS when it's off will also cause it to take longer to reestablish its location after turning it back on. This is true of any GPS unit-- the better of an idea it has of where it already is, the faster it can start tracking, because it has to determine which satellites are visible. Possibly that, combined with the interval of when it would recheck the position caused it to take so long to get back on track. Just a guess.