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Discussion Starter #1
I noticed that I've got a difference in reported speed between the HUD & DIC. I was using cruise control over the weekend. I was watching the HUD to set the speed at 55. As I set it, I noticed the DIC said "Cruise Control set to 56 MPH." And it was off by 1 mph for every speed setting I tried.

Not a major issue, but a minor annoyance. Could a rounding difference between the 2 programs.

Anyone else notice this?
 

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Re: Speed diff bet HUD & DIC

Yes mine does this also. I figured do big deal.
 

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Re: Speed diff bet HUD & DIC

Sounds like an easy software fix for GM. If they were programming it correctly, they would have one routine to determine the speed and then call that code for both the HID and DIC. They might be doing that...but when they bring back the variable, they could be rounding or using a different kind of variable (single, double, integer, long, etc.)...which could bring back results with a difference of 1 MPH.

I would report this to GM...they should be able to troubleshoot the problem very easily and get a fix into the software...if they chose to do so.
 

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Re: Speed diff bet HUD & DIC

I have the same most of the time - a 1MPH difference.

I chalked it up too the fact that the HUD shows what you're *actually* going, while the DIC shows what the cruise control *wants* it to be. It's more likely to be dead-on if I'm on flat road or going down a hill, but when the engine has to work a little harder to keep the speed, it's not that much a surrpise that it's a little off. It's a little like the Little Engine That Could ... it's trrying to keep the right speed, but is coming up just a little short.
 

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Re: Speed diff bet HUD & DIC

I've been driving Grand Prix's for ten years now...they both did the same thing. Sometimes the HUD would be off as much as 3mph. Since the HUD is digital, I'd consider that more accurate than the old analog. Do you guys ever experience the rare sunlight washout with the whole display? My GP does this if the sun hits it at the right angle...kinda annoying. Another thing the HUD will do once in a while is freak out with the MPH. You might see the speed jump up really fast and then go back to normal.
 

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Re: Speed diff bet HUD & DIC

wantone said:
I've been driving Grand Prix's for ten years now...they both did the same thing. Sometimes the HUD would be off as much as 3mph. Since the HUD is digital, I'd consider that more accurate than the old analog. Do you guys ever experience the rare sunlight washout with the whole display? My GP does this if the sun hits it at the right angle...kinda annoying. Another thing the HUD will do once in a while is freak out with the MPH. You might see the speed jump up really fast and then go back to normal.
I have exactly the same issues with my '97 Grand Prix GT. I'd be willing to bet all the older GM's with HUD act that way. I'd also bet most Acadia owners will notice the slight speed reading difference with their vehicles. Probably the analog versus digital thing.
 

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Re: Speed diff bet HUD & DIC

oicu812 said:
I noticed that I've got a difference in reported speed between the HUD & DIC. I was using cruise control over the weekend. I was watching the HUD to set the speed at 55. ....
I take it you were on a city boulevard or something, because where I am if you are doing the double nickel speedlimit on the highway, you will get run over.
 

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Re: Speed diff bet HUD & DIC

mine is 1 mph off as well; hopefully an easy fix at the next service department visit.
 

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Re: Speed diff bet HUD & DIC

Mine's off by 1 mph as well. I agree with Fenwah's post about it being an easy programming fix.

Having said that, the important thing is that he's correct that it may be the way an integer is processed. After all, most cars don't display two integer numbers (HUD and DIC) plus the analog display on the speedometer. Further, most of us are just used to setting the cruise based on the analog display alone and that's quite hard to guage whether the cruise is "dead on" speed or accelerating up a grade to catch up, or slowing on a downgrade and over the cruise set speed.

If a "fix" is developed, would have it changed, but I don't think it's that bothersome at this point. Almost too many information sources!
 

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Re: Speed diff bet HUD & DIC

I guess I will get in line with everyone mine is 1 mph off also.
 

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Re: Speed diff bet HUD & DIC

I agree with JohnFitz. Mine is off by 1-3 MPG depending upon how steep the hill is and what speed my Cruise is set at.

The engine will try to catch up...and usually it does get close...

I'm sure this issue is not all that easy to fix otherwise GM would have certainly gotten it figured out over the past decade+. There are smart people working at GM.

I wonder why a Lexus or Benz doesn't have HUD?

I love the technology and it would actually influence my decision on the next vehicle I buy...it's something I would really miss if I didn't have it.
 

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Discussion Starter #13
Re: Speed diff bet HUD & DIC

mitchl said:
I take it you were on a city boulevard or something, because where I am if you are doing the double nickel speedlimit on the highway, you will get run over.
Nope, highway. Just got our Acadia last Weds. Owners manual recommends keeping it under 55 for first 500 miles. Reasoning is explained in another post somewhere.

Driving 55 has been torture. It's worse that the truck is so quiet. I'm accustomed to large loud V8s, so 55 in an Acadia feels (and sounds) like 20 in my old ride. Gonna take some getting used to.
 

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Re: Speed diff bet HUD & DIC

Regarding the 1mph difference in speed...well, that's what you get when you get two different computers converting from kph to mph and then rounding off...especially after the one computer passes the information to the other. You're correct...it's in the software and is "on the list" for eventual updates...it doesn't affect operation and we felt it was better to give the information with a +/- 1mph accuracy, than it was to turn off the feature. Hope this helps.
 

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Re: Speed diff bet HUD & DIC

AHA! Acadia7j100001 has given us a clue!!

[Emphasis added from the post above.]
You're correct...it's in the software and is "on the list" for eventual updates...it doesn't affect operation and WE[/color] felt...

All of your posts are most informative. Whether you work for GM or not, and in whatever capacity, glad to have you here!
 

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Re: Speed diff bet HUD & DIC

OK Detectives...I'm only in this for customer satisfaction...YOURS!!! I'll do my best to keep up with this, but I'm sure your ability to ask questions and report issues exceeds my ability to read, answer and address. I'll try not to leave you hanging and am working to get additional eyes (and action!)on issues!
 

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Re: Speed diff bet HUD & DIC

Is it true? if so...get someone to fix the intermittent HUD display issue. It's very annoying.
 

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Re: Speed diff bet HUD & DIC

I'm convinced that this relates to similar issues as the intermittent display issues with XM and the HUD. Except for different reasons. For XM, the issue to me is if I shut off the car without turning off the radio/NAV, when I turn it back on after restarting, I don't get XM info displayed. If I turn off the radio before shutting down Alice/Acadia, the XM info comes right back when restarting. Now that I've got this diagnosed, I'm not having the issue at all.
 
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