I would like to know how to program this speedometer. My wheel size is 400.12

What sensor ? VSS - vehicle speed sensor on the transmission ? Colud be the speedometer gauge is bad . Do you know how the insturment cluster get's that info. ? Your best bet , take it to a qualified repair shop . You have no idea how it works , don't have the diagnostic tool's to find the problem ,so do yourself a favor . The first step would be to hook up a factory or professional type scan tool to see if the VSS info is seen in the VCM ,then to see what the VCM is sending over the serial data network . Do you know what a serial data communication network is ? VCM is vehicle control module .
Speedometer and Odometer Circuit Description
An electronic speedometer is standard equipment on all models. Integrated circuits control the air core speedometer and the stepper motor odometer. Removable bulb and socket assemblies provide the lighting. The socket assembly inserts into the back of the instrument cluster.
The speedometer system consists of the following components:
• The instrument cluster
• The vehicle speed sensor (VSS) calibrator
• The VSS
• The related wiring
The VSS calibration is part of the VCM that changes the analog output from the VSS to a digital signal. The digital signal contains 4000 pulses per mile (PPM) for the instrument cluster. The VCM sends the signal to the speedometer through CKT 389. The VSS calibration matches to the final drive and the tire size of each vehicle. Reprogram the VCM with the proper VSS calibration if the final drive or tire size changes for any reason. The signal will not be accurate for the proper speedometer/odometer operation if the necessary change is not made. An incorrect VSS calibrator can also affect the following components:
• The antilock brakes
• The vehicle control module (VCM)
The cruise control systems
The VSS calibration is programmed into the VCM. Do not service the VSS calibrator separately.
The VSS is a permanent magnet signal generator that sends an analog signal proportional to the propeller shaft speed to the VCM. The VSS mounts to the transmission tailshaft extension housing on the two-wheel drive model. The VSS mounts to the transfer case output shaft housing on the all-wheel drive models.


Use a Scan Tool in order to read the vehicle control module (VCM) diagnostic trouble codes.
Are there any vehicle speed sensor related trouble codes?
Testing an not guessing fixes problems

Maybe size of wheels?

Have you changed tires/wheels to a different size than was originally specified for this car? That will throw the calibration of your speedometer off. Sometimes the onboard computer can be adjusted to fix this, but you need garage professional programming equipment to do something like this if it is possible to do at all. Otherwise, if your speedometer is off and you haven't changed anything, it may need to be replaced, or the sensor on your drivewheels. Check with a mechanic.

check wheel and tyre sizes with the homoglonation certificate ,could be that the profile on the tyres is the wrong size .

Most certainly does
You need a different gear in the trans or transfer case,that drives the speedo
Now if the speed sensor is the output,then you will need help. I personally do not know, if a scan tool can reprogram the ecm/bcm etc, to correct for the tire change.

Ask that question next.

Ask for Size: 195/65R15

The proper size is 16 this is the genuine size of the wheels the bigger wheels will alter the speedo but if you go to a car spares shop you will be able to buy a speedo drive that compensates for the different size wheels so this option would be cheaper than replacing all the wheels so i would get this looked at first.

Let me know how you get on or if you need further assistance ok

There should be a sticker on the door near the latch with tire sizes recommended for that vehicle. last # is wheel size (14, 15, etc) This is also the size on the tire itself (205-75-15 is a 15" wheel) Then all you need is to match the bolt pattern. Any wheel retailer knows correct size or buy from someone who has same vehicle. Don't exceed recommended tire sizes unless you intend to also change speedometer to match the new final drive ratio.

the tires & rims that come with your vehicle are designed to meet all the specs of your vehicle. When you change sizes and styles, you then need to get the computer re programmed with the tire changes you have made. It affects your speedometer, your transfer case, your fuel (mpg) and the performance of the engine to the wheals. Also you can damage your transmission and rear end. So my advise is to buy a high end tire that meets origional specs. Look at the Toyo's they are great tires, great performance and no alterations are needed. Pluss they look cool as hell so try that
http://www.treadepot.com/
check this site out and call them, they have better deals on the phone and have fricking great prices on tires.

Let me know how it goes.

tepfy