Hello everyone,

About a month ago my factory NAV system started to act up. It would track me on the right road but not at the right place (seemed slow). Sometimes I can just turn the car on and off and it would put me at the right place again. More recently it shows me in a completely different area, like 5 miles away. Even if I adjust the location to where I am it seems to lose track of me after 5-10 minutes of driving. Dealer said they reinitialized the NAV but it worked until I drove back to work. Does anyone know where the NAV antennae is? I have an aftermarket system with Sirius tuner mounted on the dash, can this distrupt the NAV? This hasn't happened since I owned the car (Oct 03). Any thoughts?

 

The factory Nav antenna is located within the dash on centerline, just above the temp display unit. If you have anything at that location which could obstruct, you probably have found the source of the problem!

<font color=blue>'04 G35S 5AT, Black Obsidian/Willow, Prem/Nav/Sat</font color=blue>

 

hmm, you sound right, it could be his radar detector blocking the signal...

<font color=green>-Rambo</font color=green>
G35c-6MT-DG/Willow/HyperGround/BorlaExhaust/350Z-intake/AVIC-N1-double-din

 

my mom last car (mercedies ml320) had a weird nav problem kinda liek that when we first got the car that took forever to get fixed. Our nav said that we were in the gulf of mexico all the time (we live in houston texas) and no matter where we drove we were juts a triangle in the middle of a huge blue screen. they finally fixed the problem, but then it would get off a little sometimes and they had to fix it again. I dont know what they did, but the dealer as eventually able to fix it after we brought it in 3-4 times

2004 Black on Black g coupe 6spd.... aluminum pedals, clear corners, z tube, and pop charger. soon to have 19" volk gt-c's and PIAA xtreme whites in the clearance and corners
Houston Texas

 

Press Map and D/N at the same time until it beeps. This will enter you into Navi diagnostic mode. I don't have it in front of me, so I can't be certain of the steps, but you can actually calibrate the nav from one of the subsequent screens. ie if it tracks you slower than you're really going, thinks you're making bigger or smaller turns than in reality, etc. you can calibrate it to your speed and steering. Mess around with those for a while, and see if it helps.

G

2003.5 Black w/ Willow G35
Premium / Sport / Aero / Winter / Navi / Tint
<font color=blue>Z-tube, Pop-charger, Borla True-Dual Exhaust, Eibach Pro Kit, GroundingGear</font color=blue>

 

Thanks for the info. I'll give it a shot. I also have my Terk (Sirius Antenna) in the middle of the temp. display. Can this cause signal disruption? I thought it might and moved it away for a quick drive but it didn't seem to change things...

 

If I remember right the NAV unit only uses GPS to locate you when you start the car. it then uses the car's sensor to navigate through the maps (I.E. electronic compass, Speed Signal). It periodically checks the GPS signal for accuracy, but does not rely on it. For example, the people who have inserted a switch in the speed signal wire complain that while the switch is in the 'off' position (allowing programming while moving) that the NAV screen doesn't think the car is moving anymore. This would not be the case if it was purely GPS based.



Kevin
www.KPtechnologies.net
AIM: KPiersonTec
04 DG Coupe / VDC Memory
OEM Remote Window up mod
Procharged / Crawford / TS

 

Yep. The GPS will correct the position at least once a minute, but the majority of the input the unit receives comes from the car's sensors.

G

2003.5 Black w/ Willow G35
Premium / Sport / Aero / Winter / Navi / Tint
<font color=blue>Z-tube, Pop-charger, Borla True-Dual Exhaust, Eibach Pro Kit, GroundingGear</font color=blue>

 

Ok, I think I've eliminated it down to the GPS antenna. I entered diag mode and adjusted the longitudinal/latitude position to my location. Drove around a couple times and adjusted the speed error correction (%) to about .5. Seemed to catch up just right. What I notice is the little satellite icon on the upper left of the screen is grey and doesn't seem to sync up with the GPS to check up my real position. Even when I select "GPS Information" it says Out of Range for the satellite. After I shut off the car the GPS will put me back to an unknown location. For instance, Inglewood when I'm down in Costa Mesa. I adjust it again, and same thing. Now my GPS clock says 0:00 and cannot auto adjust... Ok I'm taking it to the dealer again...

 

<blockquote><font class="small">In reply to:</font><hr>

Yep. The GPS will correct the position at least once a minute, but the majority of the input the unit receives comes from the car's sensors.

<hr></blockquote>
I'm curious what your information source is for this. Do you have a reference manual or inside knowledge? Can you be specific with respect to GPS and speed/heading update rates that the Nav uses?

<font color=blue>'04 G35S 5AT, Black Obsidian/Willow, Prem/Nav/Sat</font color=blue>

 

My information comes from experience-- our driveway in Indy's a canopy of trees for about a hundred yards. I'd start the car, go down the twisting driveway, and turn onto the road. By the time I got to the road, the GPS would be off by about 30 feet. Then I'd turn on the road and make a left at the first stop sign. After about 50 yards, the trees are gone... and my GPS would still be off by about 30 feet. Now, there are two parallel roads, I'd just be on the wrong one. A minute or two later, my car would snap back to the correct road. Happened every time I drove out of there.

Also, when exiting a parking garage, my Nav would sometimes have me on the wrong street. After just sitting at the exit, it would snap back to the correct position once I was exposed to the sky.

If the nav doesn't have a clear signal, it'll just estimate. The signal is in constant flux, never always at its peak, so a lot of the time it's just guessing, based on speed and direction. Once it gets a signal, though, it'll snap you back to reality.

G

2003.5 Black w/ Willow G35
Premium / Sport / Aero / Winter / Navi / Tint
<font color=blue>Z-tube, Pop-charger, Borla True-Dual Exhaust, Eibach Pro Kit, GroundingGear</font color=blue>

 

seems to me that it should be more accurate if it works with speed+gyros....

the real reason that all navigation systems these days use speed pulse signal+gyros is NOT because loss of signal, its because of 3D navigation. Roads are not flat, however, maps are and so is the GPS signal. So if you are going up or down a hill, you are actually traveling faster than what the GPS signal would represent (simple trigonometry) and so the system uses the speed pulse and gyroscope to "normalize" your position.

Says so in the Pioneer gps manual and i assume that Infiniti's works (which is made by a 3rd party like all car manufacturer's nav systems are)

<font color=green>-Rambo</font color=green>
G35c-6MT-DG/Willow/HyperGround/BorlaExhaust/350Z-intake/AVIC-N1-double-din<P ID="edit"><FONT class="small"><EM>Edited by ramborami on 07/12/04 01:58 PM.</EM></FONT></P>

 

GeoBau,

I appreciate your observations. I still don't know how you figured that the GPS updated "at least once a minute"! It will actually continually update as long as a satellite signal is available. Judging from other commercial GPS receiver capabilities, it can do this at a minimum 1 Hz.

As for GPS errors, 30 feet is about the best that commercial GPS can do. And even to get this requires a clear view of four of more satellites (3-D positioning).

Now what does the system really do? From the Service Manual: It actually uses three sources of information, and it uses all three at the same time, varying the priority given to each according to preset criteria. The first source is of course the GPS signal itself, and this is given priority in higher speed driving. Second, as everyone here is saying, is the speed rate and gyro signal, which is given priority in low speed driving. But third, and not so obvious, is what Nissan calls "Map-Matching". This relies on the assumption that you are actually traveling on a known road. This is a powerful assumption, since roads consitute only a tiny fraction of the possible land area. It's this Map-Matching function that always wants to position you on a road.

Another little thing that the system has is an "automatic distance fine adjustment function". When your tires wear down, and the speed/distance calculation starts to deviate a little, it uses the GPS function to recalibrate itself. How about that!

<font color=blue>'04 G35S 5AT, Black Obsidian/Willow, Prem/Nav/Sat</font color=blue>

297926-mapm.gif

 

That's why I said "at least" once a minute [img]/w3timages/icons/smile.gif[/img] I made pains to point out that I was travelling on a road parallel to another, as I assumed most people knew about map matching, and I would receive "Well, it just put you on the road, logically." responses. I already was on a road on the map, just the wrong one.

Perhaps my Nav's a little slow, then... it usually takes a little while for it to correctly place me on the road. Also, go ahead and initialize your nav location (it'll set you in the middle of Cali) through the diagnostic mode, then see how long it takes for it to figure out where you really are. Though it may be a >1Hz system, it still takes quite a while for it to place you correctly. Try placing your car about 100 yards from your actual location on the Nav (correcting location), and see how long it takes to correct it. If it takes less than 10 seconds, I'd be quite surprised.

This makes me assume that while the sytem has the capability of running continuously, it instead relies primarily on map-matching and input from the car's sensors, then checks GPS occasionally as a tertiary measure to ensure accuracy... but those are just my conclusions based on a few tests of the Nav system.

G

2003.5 Black w/ Willow G35
Premium / Sport / Aero / Winter / Navi / Tint
<font color=blue>Z-tube, Pop-charger, Borla True-Dual Exhaust, Eibach Pro Kit, GroundingGear</font color=blue>

 

What you are observing is consistent with this otherwise strange statement in the SM:

"Position correction by GPS is not available while the vehicle is stopped."

There is no reason that it couldn't be available. But this seems to be the way the system is biased. As I said above, the Nav tends to rely on the Speed/gyro input at low (or zero) speed.

<font color=blue>'04 G35S 5AT, Black Obsidian/Willow, Prem/Nav/Sat</font color=blue>