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Sporadic "dead reckoning" issues

Discussion in 'Gen 2 Prius Audio and Electronics' started by Lutzbone, Sep 7, 2008.

  1. Lutzbone

    Lutzbone I play the trombone

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    Hello all,

    I have a wonderful 04 Prius with almost 100k miles (!) on it. We've been around the US as I'm on tour with Cirque du Soleil. I have an issue with the nav system - the "dead-reckoning" system seems to be really flaky. Sometimes it tracks perfectly, and other times it has me going thru fields, buildings, and even bodies of water! Sometimes it even says I'm turning in a circle when the vehicle is STOPPED. As long as I have GPS signal (most of the time), it will usually fix itself within 20-30 seconds, but many times this causes me to miss a turn or two. I've searched for an answer to this problem, but either I'm not typing in a good search string, or this isn't a common problem. I have tried both of the calibration options in the Setup menu (Tire change and Position/Direction), and they usually help for a while, but it eventually repeats the problem. I asked the Toyota dealer about this when I took it in for the last 5k service, and he said that he's heard of this problem with people who travel extensively - something about the nav "getting used to" a particular area and not working as well when away from "home." I looked at the Location screen of the Service Menu, and saw there were a few options that could be reset: "Distance per pulse," "Gain coeff." and "Map Matching." Anybody know if it would help or hurt to reset any of these values? Or should I just keep recalibrating thru the Setup menu? Any help is greatly appreciated!
     
  2. qbee42

    qbee42 My other car is a boat

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    The dealer's comment was rubbish, but that's often the case.

    Just so I understand your problem, let me some some statements. You correct them as necessary:

    1) Your Nav system works fine after recalibration as long as you have a good GPS signal.

    2) Over time, the calibration drifts off and the Nav gets flaky, even with a good GPS signal.

    If these are true, then that's very odd. The dead reckoning portion of the Nav system should only come into play when you loose the GPS signal. For example, on first starting the car, you may see yourself driving through a field or going off on an angle. This is because the GPS is still aquiring the satilites. As soon as a good fix is obtained, your position should snap onto the current road and all will be well.

    I'm suspicious that your aren't getting a good signal at all times. Dead reckoning is only marginally effective, and only for short distances. If your GPS signal drops out for more than of few seconds things will get progressively more wierd.

    Tell us a bit more about where and when the failures occure.

    Tom
     
  3. Lutzbone

    Lutzbone I play the trombone

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    Hello Tom, and thanks for replying!

    I don't know if it's a signal issue; the GPS screen in the service menu says I'm locked into 4 or 5 satellites most of the time (3D status). I will check on the signal strength tho. What is the normal range of signal strength?

    The thing that has me thinking it's a dead-reckoning problem is that it will randomly start turning when I'm going straight. In fact, it often says I'm turning when I'm stopped at a red light. Then when I go, it thinks I've turned and puts me on the wrong road going the wrong way. After a few seconds, it always corrects itself (unless I don't have GPS signal, in which case it will of course continue to wander aimlessly). It really seems like a gyro and/or compass issue to me. What I'm wondering is how to recalibrate that part of the system. anyone know if it can be done, and how?

    Thanks again!
    Jim
     
  4. qbee42

    qbee42 My other car is a boat

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    It does sound like a gyro issue, although I'm surprised that a bad gyro signal can influence the GPS signal. Does this happen out in the open, away from trees, mountains, and tall buildings?

    Tom
     
  5. Lutzbone

    Lutzbone I play the trombone

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    Yep, happens everywhere. Hey, just noticed you're from Northern MI! I grew up in Mt. Pleasant and went to school at CMU... small world! My parents also drive a Prius around Mt. Pleasant...
     
  6. Lutzbone

    Lutzbone I play the trombone

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    Anyway, got off topic there... Any idea if I could do any good (or harm) from the Location screen in the service menu?
     
  7. qbee42

    qbee42 My other car is a boat

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    I can't see where that would help at all. From your description, I think you have a failed or failing component in the Nav system. Have any error codes been registered?

    Tom
     
  8. Lutzbone

    Lutzbone I play the trombone

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    I'm not sure... after a quick search of the forums, I couldn't find an easy and free way to retrieve error codes. Can you point me in the right direction on this?
     
  9. qbee42

    qbee42 My other car is a boat

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    It's done at the shop, or with any of the scan gauge type of instruments. They plug into a socket under the dash.

    Since you aren't already familiar with this, you probably need to take your Prius to a shop or parts store and have them pull the codes. Some of the Prius systems are very specialized, so it's possible only the dealer will be able to help. I would take this one to the dealer.

    Tom
     
  10. patsparks

    patsparks An Aussie perspective

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    Sorry I can't help with this issue but with my TomTom XL ONE GPS sometimes the maps aren't 100% accurate especially in remote areas or a road has been relocated and that can see you "driving through fields", but mostly it is spot on. 4 or 5 satellites seems pretty poor, I normally pick up 8 to 10 with the TomTom. I never heard of a gyro in a GPS but I don't get out much.
     
  11. KMO

    KMO Senior Member

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    The gyro and speed sensors are in use all the time. If they're sending the nav system false data, it will believe them, until the conflicting data from the GPS overrules.

    The system continuously monitoring the sensors, the GPS and the map information to determine what's happening. The sensors are higher-resolution than the GPS, and give orientation information the GPS can't. But they have long-term drift. The GPS is low-resolution, but can give absolute position with no drift. The map is a useful clue - you're more likely to be following a road than going cross-country.

    The combination of the 3 information sources are put together to achieve the best results.

    For example, if it detects a 90 degree turn from the sensors, it WILL take your cursor straight off of the road the map says you're on, as it can sense you're not following the road. A non-sensor-equipped unit wouldn't do that if it didn't know the road turned onto - it would have to wait a while until it could be sure that the apparent deviation from the road wasn't just a measuring error due to the low-res of the GPS.

    If your sensors are wrong, it will perform much worse than a GPS-only device, due to the conflicting information. It sounds like the user-visible calibration options aren't helping. I don't know whether you could bugger it up with the service menu. But it sounds like there's a real fault, and probably not something you could calibrate your way out of. I wouldn't expect the sensors to suddenly drift out of calibration but still be functioning adequately.
     
  12. jrfaris

    jrfaris Member

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    We have a similar problem with our Prius. For us it seems to occur a bit more often in the mountains/forests but it sometimes occurs in the flats. It is very intermittent, maybe happening once or twice a month, but it can repeat several times in one day. It seems like a sat signal problem to me because it has us running down the wrong road, spinning aimlessly in the middle of a field or heading off cross country. I've not tried any of the service menu options.
    Anyway, is there any chance you have a lockpick unit from coastal electronics installed? It's a unit that allows you (your passengers) to enter destinations while you are moving. It does so by disconnecting the gps signal for a short period of time to make the car think it's not moving. We have one and I'm considering removing it to see if that if it may be what is contributing to the problem. Unfortunately, it really is a nice feature and living without it for long enought to diagnose the problem will be inconvenient. Just wondering. If you don't have one then I may also looking for the other solutions.
     
  13. blazer_5154

    blazer_5154 Heh, you said "member"

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    Just a casual observation, it sounds to me like it could be an intermittent / shorting connection or a bad component as previously suggested. Have you checked all of the connections to the GPS unit? Perhaps some of the wiring harnesses are not properly "seated" and are only making sporadic contact, confusing the signals to the GPS unit. Once again though, I am grabbing at straws just as much as the next guy, but it would be the first place I would start checking. BTW I am going to see a "Cirque" show in a couple of months in the DC metro area at National Harbor, will I see you there?
     
  14. jrfaris

    jrfaris Member

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    That's a good suggestion. I just tried reseating the connections on the DVD unit under the driver's seat. For us, that's where the Lockpick add-on is. I didn't see anything obvious but we'll wait a while to see if the problem re-occurs. Maybe it won't.
     
  15. Lutzbone

    Lutzbone I play the trombone

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    Hi all, and thanks for the replies! Here are some updates/responses:

    1) I got into the diagnostic menu mentioned here, here, and here. I got the following codes:

    NAVI:
    Code: Sub-code:
    01-DD 110-00-6
    01-D6 -00-B

    There are others in the G/W (gateway) and EMV (MFD) screens, but I thought these were the most pertinent starting point. Anyone know how to decipher these?

    2) I do not have a lockpick

    3) Checking the connections sounds like a great idea, can someone help me with how/where? Perhaps my trouble codes above can confirm/refute this suspicion, but it definitely feels like a "short circuit" issue. Today, the nav system was on its best behavior... :rolleyes:

    4) Yeah Blazer! I play trombone (plus bass trombone, keyboard, percussion/sound effects etc) in Kooza, the latest Cirque big top tour. We will be in DC at National Harbor, starting at the end of October. Hope to see you there!
     
  16. blazer_5154

    blazer_5154 Heh, you said "member"

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    The GPS unit is located underneath the driver's seat. You should be able to access all of the wiring harnesses / connectors by sliding the seat all the way back. I would also check to make sure that all of the individual wires are properly seated inside the harnesses, it wouldn't take much to cause the kind of behavior that you are experiencing. I would also be concerned that some of the individual components and / or sensors may not be properly soldered, much like the MFD problems that some owners were experiencing in earlier models. If that is the case, you will either have to submit it for warranty / recall or take the highly technical and electrically irresponsible method of fixing it yourself.

    My fiance and I will be attending one of the Saturday performances of Kooza in October, if you'd like, PM me and I'll give you my information; maybe we could meet for lunch while you are in town.
     
  17. Lutzbone

    Lutzbone I play the trombone

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    Cool, I'll check it out. I also found some threads that mentioned the location of the GPS sensor as being on the left side of the dash. I did have a parking decal near the sensor (though not over it) which I removed. Since I did that and went in the diagnostic menu (I didn't clear any codes or reset anything), it's been on best behavior... Keeping my fingers crossed that it's really that easy!