Snopczynski

I have my truck in the shop for the 2nd time in a month trying to get them to recalibrate my speedo and figure out why my overhead mpg display is off by 2 mpg.

Basically when my truck is going 62mph on the speedo, it is actually going 60mph on gps. Its been checked with 2 gps units and both found that it is off by about 4%, at 35mph on speedo, the truck is actually going 34mph.

The overhead shows when I fill up that I got 17.1mpg, but miles travelled divided by gallons put in tank shows 15.005 mpg. I reset everything on the overhead on fill up and dont touch it till I fill it up again.

The Dodge dealer has told me twice now that everything is in working order and calibrated to Dodge specs. I spoke with the shop foreman and he says all he can do on a 2007 is recalibrate rear axle ratios.

I figured out if I fill the truck up twice a month, that at the end of the year it will have 456 miles more on the odometer than the truck actually travelled. By the end of my 53 month lease it will have an extra 2,731 miles on it than it actually travelled.

Anyone got any ideas on what to do, or had this problem with a 3rd gen?

tbarbee1

I was about to type, so what then I saw the key word LEASE. Mine is off at least that much and every truck I've ever had has not been dead nuts accurate. If you didnt have GPS you wouldn't have any idea that it wasnt perfect. My overhead miles driven are the same as the odometer. But the overhead mpg is 2-5 miles off from hand calculated. I will be surprised if they get it any closer than it is. Hope this helps to know you are not the only one.

Food for thought....... buy a programmer that will change tire size and adjust the tire size until it matches the GPS.

Danderson

I'm running 285-70-17's with a manufacturer supplied height of 32.7". With Smarty I corrected it to that tire height. It was way off! I had to reset it for 32.3 and my odometer is still off by 2%. My suggestion is to just deal with it and keep that truck out of the dealer.

Snopczynski

I did have an idea it was off, thats why I did check it with the gps.

If I can get a programmer and change the tire size, shouldn't the factory scan tool be able to do the same?

tbarbee1

One would think but I tried three dealers who couldnt get mine right before I bought a programmer that would change height in 1/4 inch increments and its right on now.

Snopczynski

Its been real fun, last time it was in for the speedo issue I got the usual everything is ok, and all parameters are to spec. This time I leaned on the Service Manager, the shop foreman, the advisor, and even my salesman about it. I also let them know I was a Master certified ASE tech and worked for Audi and now GM. This afternoon the shop foreman said they would keep it another day and call dodge techline (STAR) on it in the am tomorrow. So, right now I am stuck speeding around in the Pinto Cruiser loaner car. The foreman also told me that when he was going down the road in it with the scan tool the speed signal matched what the dash was saying. I was thinking, you friggin idiot, then I told him thats because the ecm needs to be recalculated to give the speedo a different indication signal. He said, yeah your right. I told him the gps is in the center console of the truck and he was more than welcome to use it. He said he just might do that tomorrow.

Dodgezilla

Mine's the same way... I'm not too worried about it though...

Snopczynski

The shop foreman at the dodge dealer called me this morning and said he changed the axle ratio setting, went to one of the tire size options he had to choose from and changed some sort of abs rotor setting and got my speedo within .5mph of being accurate on the gps. Now its on the other side too, so its going .5mph faster than the speedo says. He also said it ought to make the overhead a little more accurate. He told me for the most part the overheads are not accurate at all and there wasn't anything they could do for me besides trying to make my speedo read correctly.

I would think that the trans uses rpm, and the speed signal to determine shift points. I am gonna call him though and make sure it is still shifting ok.

LongRanger

Your figures match mine, off a little on the speedometer and sometimes 2.5 mpg off on the overhead. My understanding is that Dodge did a flash that supposedly increased mileage but mostly changed the readings on the overhead to make things look better. As far as the speedometer, most vehicles read a little faster than actual, not just Dodge trucks.

SolarExpress

The little portable radar trailers must be off too. Every time I pass one, my speedo is dead on what the trailer is displaying. If we're both off, well, at least my truck agrees with the local law endforcment. Also, I was going to mention the ABC controller. It uses revolutions per mile instead of tire size and or axle ratio. Whenever I have upsized my tires in the past, I've given my dealer the new RPM to enter into the controller.

Snopczynski

They fixed mine, they got it within .5mph on the gps at 60 mph on the speedo. The shop foreman said he changed axle ratio, tire size, and I think he said something about abs rotor teeth count. They still claim no reflash or update for mileage or the overhead.