1992 Ford E-Series Van Error code on speedometer?

Refer to SPEEDOMETER CALIBRATION TOLERANCE SPECIFICATIONS table. Check odometer calibration. If both odometer and speedometer are incorrect in the same direction, it is usually a sign that the conversion constant, tire size or speed sensor ring are different than programmed. A speedometer inaccurate with an accurate odometer is usually a problem with the speedometer module itself. If speedometer and odometer are within specified limits, speedometer is normal. If not within limits, go to next step.
If ERROR 3 message alternates with normal odometer display, go to step 6 and reset conversion constant referred to. If ERROR 3 message does not appear, go to next step.
If tires are the same size and properly inflated, determine conversion constant and go to step 5. If tires are different sizes or improperly inflated, correct condition and go to step 1.
Use the following procedure to check whether conversion constant in speedometer is correct.
Press and hold RESET button on front of speedometer while turning key to RUN.
Release RESET button. Pointer will prove out and some codes will appear on odometer display. If an "E" is on the left side of display, module is programmed for English display mode and should have English (MPH) graphics. A lower case "o" signifies overseas (km/h) graphics. Verify that graphics and display mode agree
if tires are different sizes could cause this as well as a dash problem or speed sensor/wiring issue