Help with Speedometer adjustment.

Now you are throwing a wrench in the works....

ECU stands for "Electronic Control Unit"....so you might need a new cable.

Or you could just buy a new truck and not worry about the piddle stuff!!!

 

the ecu or ecm is where most of the trucks speedos are done. like otherhalfw said reflash for tire size rear ratio and so on.

 

You can use a handheld or laptop, and change the tire revolutions per mile settings, which will change the speedo. I changed mine a couple times until it got as close as possible. Not 100%, but real close.

Almost all speedos are fast. I think it is to run warranty out sooner.

 

Now you know they use the west bound side of Donner and Cabbage to figure MPG in these big rigs!

 

I bet your getting close to real answer now???

 

The dip switches is what adjusts it. Go to the dealer and pretend to buy a new speedo. In the box is a piece of paper telling you the correct pattern for them switches to match your truck setup. You probably have one or two switches in the wrong position. Someone probably put different size tires on that truck. They are similar to them switches in garage opener remotes. Piece of cake.

Most trucks I ever been in reads 2 mph over according to my GPS and the construction speed limit signs. My new truck is set at 65 but reads 67.

DOT regs require speedometers to be accurate within +/- 5mph. So you're okay there.