Ford Power Stroke Nation banner

1 - 8 of 8 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
i have a 96 f250 2wd. I lifted the front and put some 275-65-20's on it. But now my speedometer is off how can fix this?
 

·
Registered
Joined
·
5,373 Posts
There's a recalibration procedure; some trick you do with the SELECT and RESET odometer buttons. There's a calibration number it uses to calculate, and it displays it on the odometer and there's a way to change it. [email protected], I forget where, but ONE of the forums has the instructions, including what number to use for what tire size (or at least based on the overall outside diameter of the tire). You just gotta start searching, something like "PSOM calibrate" or "speedometer calibrate" or something.

One thing I do remember is that you can only do this so many times, I wanna say six times, EVER, on the cluster. So if you're gonna be changing tire sizes often, you'll just have to put up with it.
 

·
Registered
Joined
·
5,958 Posts
Here is the write up that Steve Baz did years ago and can be found on Baz's Page.



Recalibrate Your Speedometer After Changing Tire Size

There is no tire size/code chart because tire size vs. actual tire dimensions are different between manufacturers. Even between the same tire size and same maker there will be a difference in actual size between the different tread designs.

The Ford calibration equation is:
20186 / tire height in inches = some number, then: some number /.6666 = program code

Example:
Start with 20186, divide by actual tire size in inches. Divide again by .6666

You want to use a rolling measurement to get your actual tire height (If you try to measure the tire in the driveway, use conversion charts, or anything else you will end up with an inaccurate reading again). Use your rear tire since the sensor is located there. Mark the ground and your tire and roll forward 3 times marking the ground each time. (I ran over a spot of oil at a local gas station and measured between my tread mark prints), then divide that number by three to get the average length of one revolution (this will protect yourself against a bad reading using just one revolution). You can then divide the length of one revolution by 3.14 to get actual tire height. Be careful in your measurements, a small amount will change the code. EX: 31.69" tire height is code 956, and 31.21" tire height is code 970.

Now, to program it into your truck:

Warning: You can only change the calibration 6 times without replacing the module.

To set the calibration, ground the single wire connector under the glove box it says PSOM (Programable Speedometer Opdometer Module). ”Yes there is only one and it has a spade type plug on the end". I used a wire with clips on both ends to ground the plug to a screw under the dash or try a test light and use the clip end to the PSOM and the other jam in a dooe hinge. Now look at your speedometer on the face of your dash while sitting in the drivers seat and there should be a "reset" button and a "select" button. While holding the reset button in on the trip meter, turn the ignition to 'on' while the wire is still grounded. Let go of the reset button. The speedometer display will sweep once and will show a code of some kind then push in again the "reset" button and the existing code will be displayed with RECAL?, mine said 976 RECAL? Now you enter your new code you came up with by dividing the rolling measurement by PI or 3.14 by pushing the "select" button until it gets to the new calibration code number. You may have to push “select” a whole bunch of times until you get to your code. If you turn off the key at this point the original code will not be changed or any of the 6 lives will not be used. To store your new code press “Reset”. Turn off the key. Unplug the ground wire. To check the new calibration, use the mile markers on the interstate. Run an indicated 60 mph and it should take exactly 60 seconds to go 1 mile.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #4
ok cool thanks
 

·
Registered
Joined
·
38 Posts
i don't have a reset or a select button on the dash. i just have the push button for the trip odometer. I don't have the digital display. Any advice?
 

·
Registered
Joined
·
5,373 Posts
What year/model of vehicle?

Edit - if it's the truck in your signature (BTW, sig is the WRONG place to put truck info, since members often disable sigs because of the huge waste of space/bandwidth), you should try posting to the section relevant to that year. The SD trucks obviously have some other procedure, one that the folks who only own OBS trucks wouldn't be familiar with. If I had to guess, I'd say it's probably done with a high-end communication device plugged into the OBD-II port.
 
1 - 8 of 8 Posts
Top