Speedometer not accurate.
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Fleet Mechanic
Joined: Apr 2011
Posts: 1,441
Likes: 6
From: Marseilles IL
Speedometer not accurate.
My spedo is not accurate. I used my autoenginuity to try to correct it and now I'm 6 mph off at 55 and 65. Spedo reads high. What am I doing wrong? Do I have a bad sensor? Any advice? Thank you!
Fleet Mechanic
Joined: Jun 2009
Posts: 1,866
Likes: 8
From: Fleetwood, PA
you need to go to the manufactures website for your tire. or go to tire rack.com find your tire and it will give you the correct outerdiameter size. post up what size your tires are on here and ill help you look
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Fleet Mechanic
Joined: Apr 2011
Posts: 1,441
Likes: 6
From: Marseilles IL
I made the change to 33.25 and it's off more now! Now it reads 8 mph faster! What could it be?
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Post Fiend
Joined: Nov 2007
Posts: 9,549
Likes: 14
From: Payson, AZ
Was the speedo accurate with the previous tires.
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Post Fiend
Joined: Nov 2007
Posts: 9,549
Likes: 14
From: Payson, AZ
Try the smallest tire available in AE and go from there. That's all I can think of. 
Thread Starter
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Fleet Mechanic
Joined: Apr 2011
Posts: 1,441
Likes: 6
From: Marseilles IL
I'm using my gps think it's a garmen to judge my actual speed. I'm not sure about a speed adjusting module? I never thought to look for one. Is the speed sensor on the transfercase? Other than being under the truck by the speed sensor, is there another common spot where it could be? Also I hooked up my autoenginuity and the readout for speed was accurate with the speedometer, so I will look for a little box wired in somewhere.
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Fleet Mechanic
Joined: Apr 2011
Posts: 1,441
Likes: 6
From: Marseilles IL
Ok I looked under the truck and under the dash and under the hood the only non factory item I found is what I think is a gps transmiter, a black box aprox 2" square and a quarter inch thick. It's above my spedo cluster, it has power going to it, a yellow wire streched out for an antenna I would assume. it also has a blinking green light. I cannot find any spedo correction device. Also I don't know where the speed sensor is! Is it in the transfercase? Does the speed sensor have a gear on it that could have been changed? What could be my problem? My spedo being off drives me nuts!!! Plus im sure it effects the computer some how being off? Please help! You people are awesome! Together we can do it!!
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