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Home >> Ford >> 1992 >> Explorer 4D Utility, RWD, Automatic >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Gauges & Instrument Panels >> Description & Operation >> Reset Conversion Constant >> Bronco, F-Series, E-Series Van

Bronco, F-Series, E-Series Van

  1. 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.
  2. 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.
  3. 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.
  4. 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.
      NOTE: The number appearing after the type is the microprocessor revision level and is not used in this test.
    • Press and release RESET button again. The conversion constant and the word CAL will be shown on the odometer display.
    • Verify programmed conversion constant is the same as displayed in the chart. See Fig 1. Turn ignition switch to OFF to exit test. If programmed conversion constant is the same as displayed on chart and programmed display mode matches the speedometer graphics, replace instrument cluster. See INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. If conversion constant is incorrect and programmed display mode is okay, go to step  7. If conversion constant is okay and programmed display mode is incorrect, replace instrument cluster. See INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION.
  5. Check tire size and type on vehicle rear axle or SAE average revolutions/mile. Refer to tire/axle capacity and note conversion constant. See Fig 1. If conversion constant can be determined, verify conversion constant and go to step  4. If constant cannot be determined, go to next step.
    Fig 1: Speedometer Conversion Constant Chart
    G50H16854Courtesy of FORD MOTOR CO.
  6. To determine conversion constant, perform the following procedure:
    • Hoist vehicle.
    • Measure Tire Outside Diameter (TOD).
    • Note number of rear axle speed sensor teeth, speed sensor ring diameter or axle capacity/tape group.
    • Verify speed sensor ring diameter with identification tag attached to rear axle cover retaining bolts. If tag is missing, manually count teeth. (7.5" rear axles have 102 teeth, 8.8" axles have 108 teeth, 10.25", 10.5" & 11.0" rear axles have 120 teeth.)

    If TOD is greater than 25.2", use formula revs/miles = 1528 - (28 x TOD) to calculate SAE average revs/mile. Example: 1528 - (28 x 28) = 744 revs/mile. If TOD is less than 25.2", revs/mile = 20,850/TOD. Example: 20,850 divided by 24 = 859. After revs/miles is determined, calculate the Speedometer Conversion Constant using the speedometer conversion formula. See Fig 2. After Speedometer Conversion Constant has been determined, go to step  4.

    Fig 2: Speedometer Conversion
    GB0020894
    7. NOTE: Pressing and releasing RESET button to lock in new conversion constant reduces the number of times the PSOM can be reprogrammed by one count. The module can only be reprogrammed 6 times. If it is determined the original conversion constant is satisfactory, to cancel adjustments BEFORE new constant is locked in, turn ignition switch to OFF.
  7. Reprogram speed conversion constant with the following procedure:
    • Locate dealer mode programming enable connection at the bottom of the instrument panel below the center of the glove box.
    • Insert metal clip in repair wire panel connector. Clip other end to ground while ignition switch is in OFF position.
    • Turn ignition switch to RUN (not crank) position while holding down trip odometer RESET button on speedometer. Release RESET button.
    • Speedometer will prove out (sweep across dial and back). English, Metric and revision levels will be displayed. Last number on right side of display is reprogramming lockout count. This number shows remaining number of allowable conversion constants. When count is zero, no additional changes can be made to this instrument cluster. If a conversion constant change is necessary, a new instrument cluster must be installed.
    • Press and release RESET button again and PSOM conversion constant (without decimal point) followed by the word CAL, will be displayed.
    • Press and release odometer SELECT button as many times as necessary to change conversion constant to correct value.
    • When correct new value is displayed in odometer window, press and release RESET button to lock in new conversion constant.
    • Turn ignition switch to OFF position and remove ground wire. Verify proper operation of speedometer. If conversion constant is set to desired value, procedure is complete. If constant is not set to desired value, go to step  5.
SPEEDOMETER CALIBRATION TOLERANCE SPECIFICATIONS (1)

Actual Speed MPH (km/h) Allowable Range MPH (km/h)
30 (48) 28-34 (45-55)
60 (97) 58-67 (93-108)
(1) Odometer measured over actual 10 miles (16.1 km); allowable tolerance is 9.6-10.3 miles (15.4-16.6 km).
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