Nav Gyroscope: Where is it?

I'm having a major problem with my factory nav system. Not sure if it's something with the gyroscope / dead reckoning or, more likely, the device that receives the GPS signals from the satellite.

I've had an 08 Prius for exactly a year and never had any trouble with GPS first six months. Then in the fall, the nav system would frequently "lose" me, i.e. there was no GPS signal from the satellites showing on the screen and the dead reckoning would eventually get out of whack after several turns.

When I have a GPS signal, everything works fine of course. For a few months I've been religiously watching the screen and noting when I have GPS reception and when I don't. The trouble is I estimate that I have a GPS signal ABOUT 10% of the time. That cannot be the norm!

I live in Nashville and will maintain a signal if I'm just running errands around town. If I get 10-20 miles out of the city, the signal will disappear and might never come back for hours on a road trip, even if I drive through cities like Louisville, Cincinnatti, Columbus, where there should obviously be satellite reception. I'm getting very frustrated now that my GPS has become so unreliable.

Is it possible my receiver thing is not working properly? Any suggestions would be much appreciated. Thanks.

 

It sounds like a receiver or antenna problem.

Tom

 

This is a poor man's accelerometer, not a gyro, using a crystal piezo element like that in the old time phonograph crystal cartridge which generates a voltage when the phonograph needle moves along the groove of the record which applies varying pressure to the crystal.

Instead a small weight is attached to the crystal, when making a turn a pressure is applied to the crystal by the central fugal force and a proportional electrical force is produced.

 

Follow up regarding my poor GPS signal: went to the dealer and ultimately got a quote for a new navigation antenna assembly (just the part, not the actual replacement labor) for $499.

It took a while to get someone who actually had a clue. First guy I talked to -- the supposed GPS expert among the service managers -- knew less than I did. He was trying to convince me the GPS system used the same antenna as the radio on the roof of the car. Finally, I kept talking until someone came along who knew a little more. The antenna is actually in the dash right behind the display screen.

I have been back in there before when I hooked up my XM radio, so this guy suggested to go back in there and make sure no connections got accidentally loosened. And if not, consider unplugging my XM and see if the GPS works better. He said it could theoretically be creating some interference. Has this actually happened to anyone else?

I'm past the warranty mileage so I'm kinda S.O.L. If it's just something like the wire from the antenna is loose, I'll throw a party. I'll check it out and post results. If anyone has any other suggestions, they'd be much appreciated. Thanks.

 

There have been problems with a loose antenna wire under the dash.

Tom

 

Interesting. I did go in behind the display screen this afternoon and checked the connections. Everything appeared to be in order. I pulled out the connections into the back of the nav unit and sprayed some product on the connections that has been occasionally effective when the electronics get ornery in my old 4-runner. I'm not optimistic about seeing any performance improvement based on what I did. We'll see.

Any idea where the "looseness" has occurred for others? Up under the dash at the actual antenna?

 

Will it be a BYO party or are you putting on the grog?

 

Update with good news and bad news. First the good: tested the nav system for first time after unplugging connections behind screen, spraying them with connection stuff and plugging them back in. I drove from Nashville to Athens, GA to Atlanta (almost 400 miles total), watching the nav screen intently checking for a signal, and never once did I lose the signal. That was a welcome change.

However, the bad is that somehow my unplugging and plugging back in the connections in the back completely disabled the satellite radio -- as in, it's no longer an option. When you scroll through the modes it just goes FM1 FM2 AM AUX, and when you press the AM SAT button, it just goes to AM and won't go to SAT. I'm certain everything was plugged back in and I can't figure out why just unplugging stuff would disable the SAT radio feature. I've searched for info on that here on the site but can't find anything on how to re-enable the SAT.

Regarding my GPS signal, I guess the reason it worked today is probably one of the following
A) a fluke;
B ) due to my spraying the connection stuff in there and establishing better connections; or
C) due to some type of interference the XM radio was causing with the GPS signal that was not there today b/c the XM radio was disabled for some reason.

But honestly, I'd rather have a working SAT than GPS. Hopefully it doesn't have to be one or the other. Anyone have any ideas how I can "re-enable" the SAT radio? Any help would be much appreciated. Thanks.

 

I read somewhere the Prius uses a "quartz gyro," a type of resonating solid-state gyro, for its Nav system.

I can't find it, but about 25 years ago a Toyota Mark II used a 6" fiber-optic gyro (FOG) based Nav system in Japan, which was unique in automotive applications, I think.

 

The radio checks for the presence of a satellite radio when it's turned on. If it doesn't find it, it's because it's unplugged or the satellite unit is not working.

 

Thanks for the suggestion. Unfortunately, no luck with getting the radio to recognize the presence of the XM. I checked the connections numerous times, unplugged and plugged back in, still nothing. Got on the phone with Vais Technologies (from whom I had bought the XM) and they walked me through reprogramming their device, but still nothing.

Vais said to send the SoundLink back to them and they would check it out to see if there is a problem with it.

I really can't fathom what happened, why the XM just totally disappeared. All I did was unplug the connections into the nav screen and then plug them back in. I didn't touch anything related to the XM, since that goes into the back of the radio. I just don't know. Hopefully Vais can help me. At least my GPS is working like a charm now...but I miss my XM on the long drives.

 

FYI -Here's a pic of the NAV ECU PCB located under the driver's seat and the GPS antenna located behind the dash. I don't see any component that looks like a gyro in the ECU. However, the service manual for the nav system mentions a gyro several times.

 

The gyro is combined into one unit together with the GPS antenna - at least, 2004 service manual says this clearly. Indeed, this eliminates any possibility of mechanical shift between those sensors, for maximum precision.

 

Mechanical shift between the sensors is not important. The antenna is only positionally sensitive and the gyro is only rotationally sensitive. The relative spacing or alignment between the two is irrelevant.

Tom

 

The gyroscope is located in the center console. Remove the cup holder for the back seat by pulling straght back it is held on by 4 clips. You will see a square modual there I beleave it is the gyro.
Joe

 

The unit in the center console is a yaw sensor for the vehicle stability control. It's not used by the GPS. Unfortunately I'm on a very slow connection and can't bring up the NAV board picture, but I'm pretty sure the "gyro" is on the board. As noted above, it's a solid-state unit, not an actually spinning gyroscope.

 

Unless VSC fails to do its job, in which case the gyro might be spinning briefly.

Tom

 

Actually, this is a data problem and handled by software. GPS has a good enough fix (usually within 20-40ft for the 4 in-car portable units I've used, I get 9-15' for my cheapie handheld) - but the data for the roads isn't exactly correct.

I have software that allows "snap-to" the road setting. When I disable it - it will very often show me as much as 100-200 yards from the road. The GPS is correct - the data is not. So the software has a "snap-to grid" setting, and puts you on the nearest road, corresponding to it's data.

Tiger data (the free stuff for the US) is the worst data I've seen. It gets successively better (normally a function of cost) as you go up the expense scale. Navteq data seems to generally be the best, but I've still seen different software supposedly using the same data bugger up where it thinks you are.