HOW TO RECALIBRATE FORD TRUCK SPEEDOMETERS

To recalibrate your speedometer after changing tire sizes:

Start with 20186, divide by actual tire size in inches. Divide again by 66.66.

Example:
20186 / 34.5 = 585.10

585.10 / 66.66 = 8.78

Thus for 34.5" tires, the calibration number is 878.

To set the calibration, ground the single wire connector under the glove box (often Lt. Blue wire w/ a Yellow tracer, but you might want to check a manual for specifics), hold in Reset button on trip meter and turn ignition to ON. After the speedometer needle cycles from zero to top speed and back to zero, press Reset button again. You should now see the calibration # that you currently have. From here, use Select to get proper calibration, and press Reset to store.

When you press Select, the number only goes down, but don't worry if you need a higher number. After you reach a certain number (400 or 500 I believe), it will start back at the highest number the speedo can be calibrated with (often 1100), and go down again.

Notes:

Larger tires will require a smaller calibration number.

If your new calibration number needs to be larger than the highest number allowed, just go with the highest number allowed.

If you shut your ignition switch OFF before you press Reset to store the new calibration number, the number will remain what it was before you started.

With stock 235-75 15's, the calibration number should be about 1044, but you may find that it's been set at 972 from the factory. This means that your odometer has more miles on it than you have truthfully traveled.

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

I have no idea what years this applies to, but it has been suggested that if you have a digital odometer, it applies to you. The easiest way to see is to hold the Reset button down while you turn the ignition switch to the ON position. If the speedometer needle cycles, this applies to you.

Take care,
-Chris

 

Thanks dude.

 

I did this yesterday on my truck, works great, except my numbers went up when i pressed the button, when it got to 1100 it started back over at 500. It also said i could only reprogram it 3 more times, the previous owner must have screwed with it.

-Jon

 

Select button???? Maybe this doesn't apply to me since I have a 1990?

 

What??? You don't have one??? I thought all F-150's came with a button that allows you to choose between blondes, brunettes, or redheads! You poor guy!



This procedure requires a digital odometer with a trip meter. The Select button is what allows you to switch the display between total miles driven and trip miles driven normally, and permits you to see the speedometer calibration code when this procedure is followed.

Take care,
-Chris

 

My odometer removes miles after I shut the truck down and start it again. Could it be that someone attempted this and botched it up? Or could it be that it has had flash#7 applied to it.

 

How did it tell you that? Did it scroll a message accross the odometer?

 

How exactly does it "remove miles"?

Adrianspeeder

 

This caption contains the complete procedure & all relevant info:

 

Excellent instructions, but...

I haven't changed tire size, but rather I changed the rear end ratio for towing a travel trailer. I went from the stock 3.08 to a 3.55 ratio - so what should my "magic number" go to? I'm not sure how to manipulate the math you give to figure this out.

Thanks!

 

If you read that caption, it clearly says that RAR has nothing to do with the PSOM calibration.

 

What is the single wire connector?

 

The PSOM Programming Enable connector, as that caption explains.

 

Hello PKRUD,

Thank you very much for the info.
I plan on using it.
Please help me better understand the math.
I think I understand the 20186, but where does the 66.66 come from?
I actually came up with 20168.

5280ft x 12" / pi = 20168

I have a 2011 F150 XL
I am going to go from P235 75R17
to P275 65 R18

and I want my speedopmeter to be accurate

 

Unfortunately, those posts are 14 years old and PKRWUD has since passed away.

Also, this thread concerns the PSOM system in pre-1997 trucks and does not apply to a 2011 in any way. You need a programmer to reprogram the ECU to correct the speedometer/odometer in a 2011. Don't sweat the exact math, just get it close and do your final correction with a GPS and with highway mileposts. Expect the speedo to read 61 or 62 when you are doing 60 by GPS, this is by design, the odo should be spot on.

If you don't want to buy a programmer, if that tire size was a factory option a dealer can reprogram it for a fee.