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Dan M
Dodge Dakota
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2/14/2008
13:41:57

Subject: symptoms of a bad speedo sensor
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I've noticed that the last few weeks my truck speed is off. I've compared it to my avenger and my wife's jetta. Driving 65 in the truck yields around 70 in the jetta and avenger.

I hooked up my scanner and the speedometer matches my scanner.

do I have a bad speedo sensor?

- Dan M



daddio
Dodge Dakota
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2/14/2008
14:11:47

RE: symptoms of a bad speedo sensor
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have you changed tire size from the stock size?



Dan M
Dodge Dakota
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2/14/2008
21:00:26

RE: symptoms of a bad speedo sensor
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Yes and no. I have the optional 265/75/16 tires, but it came from the factory this way. I bought the vehicle used from a dodge dealer and the original owner left me the original window sticker from the factory in the owners manual in the glove box (has a different listed than the one i purchased it from).

I've owned the truck for a few years. I know I've passed many cops driving 65 (70) and 70 (75). Maybe they all didn't care. I suppose it's possible it's always been off.

it has 87k miles.

- Dan M





dodger
Dodge Dakota
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2/15/2008
01:08:41

RE: symptoms of a bad speedo sensor
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I could be the speedometer itself. Did you compare a measured mile to the other vehicles?
A cable-less speedometer controls voltage to a motor that turns the odometer and the needle by an inductor.
If there is a resistance problem to the input current the motor will also register less miles.
The motor could be good but the little inductor coils for the needle could be out of spec.
If both speed and mileage is off then it could be the sensor.



Dan M
Dodge Dakota
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2/15/2008
05:39:11

RE: symptoms of a bad speedo sensor
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I didn't compare mile-to-mile in the dakota to another vehicle, only speed to speed as stated in my original post and the truck is about 5 mph off.

I will see if i can do a mile-for-mile test compared to fixed reference points or one of my other vehicles.

- Dan M





Kowalski
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2/15/2008
14:03:53

RE: symptoms of a bad speedo sensor
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Are you sure it's the truck that is off ? It's allowable for a speedometer to read higher than actual speed (that will keep you under the limit); but not allowable for it to read too low. Not all speedometers read exact.

Lead, follow, or get out of the way

TexasTodd
Dodge Dakota
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2/15/2008
20:06:02

RE: symptoms of a bad speedo sensor
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Dan M,

#1. what kind of scanner are you using to match your speedo?

#2. I too ordered my truck with the tire and handling pack in 2001, is this a 4x4, cause that's not what came on my truck.

I since put a taller tire on, which is 1 inch taller.
But I used my Superchips to change the tire height size to make my speedo right again by adding an inch..

But, it wasn't right just by adding an inch,
I then checked it with my GPS I use from my sailboat, and it's now Right on at any speed.



Kowalski
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2/16/2008
07:45:19

RE: symptoms of a bad speedo sensor
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Todd - he didn't use a scanner. He says he's going by 2 other car's speedometers.

Lead, follow, or get out of the way

Dan M
Dodge Dakota
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2/16/2008
17:00:25

RE: symptoms of a bad speedo sensor
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Yes I did check with my hand held scanner. Since the speed my scanner was reading was the same as the speedometer guage, that tells me my guage is working properly and it's really the speed that is off.

Yes, i compared to 2 differnet vehicles and it's 5 mph off on both cars.

- Dan M





Cuda
Dodge Dakota
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2/16/2008
17:36:24

RE: symptoms of a bad speedo sensor
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Does anyone know the torque spec for the front hub nut?
This is for a 2002 dakota r/t



Kowalski
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2/17/2008
08:01:13

RE: symptoms of a bad speedo sensor
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If the scanner and your speedometer agree, that wouldn't mean the speed is off. That would mean the 2 car's speedometers are off; as I tried to point out in my first post to this thread. The government allows speedometers to read high - but not low.

Lead, follow, or get out of the way

Dan M
Dodge Dakota
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2/17/2008
19:02:29

RE: symptoms of a bad speedo sensor
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Kowalski - I'm not understanding. Wouldn't the obdii scanner read the same speed as the speed sensor? Wouldn't it just pick up the speed directly from the speed sensor via the computer, not from the speed gauge therefor removing the dash gauge from the equation? I thought this would tell me that the dash gauge is reading the same speed that the speed sensor is putting out and it is not displaying a speed different than the speed sensor?

I guess one thing to do would be check the speed of one of the 2 cars with the same hand held scanner. If the car speed matches the scanner then that points me to my original thought, the speed sensor is wrong in the truck.

- Dan M



Kowalski
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2/18/2008
18:39:14

RE: symptoms of a bad speedo sensor
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My bad on missing what you said about the scanner in first post when replying to Todd's post. I think Todd may have been wondering if you were using a GPS when you said scanner; and that's what I thought of when he brought it up. A GPS would show which is correct. I think you're basically right about the obdii scanner, now that we're all on the same page on that. But checking a car with the scanner could just give the same reading as the car's sensor is telling it; without really telling which one is really the correct speed. Just like you surmised it could be doing with your truck. You could look for a traffic radar sign like they sometimes put up, that would give a good idea as to how accurate yours is too.

Lead, follow, or get out of the way

Dan M
Dodge Dakota
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2/19/2008
08:30:57

RE: symptoms of a bad speedo sensor
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Kowalski - I was beginning to wonder about you...

I haven't done anything with this yet, I've been fighting a furnace at home since friday.

- Dan M



dodger
Dodge Dakota
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2/20/2008
20:05:16

RE: symptoms of a bad speedo sensor
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If you could get the schematics you could put a multimeter on all the power sources to see if they are out of spec.



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