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Test F: Speedometer/Odometer Inaccurate

WARNING: This page is about a different car, the 1997 Mercury Grand Marquis and 1997 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.
  1. Road test vehicle. If speedometer is operating, go to next step. If speedometer is not operating, go to step 5).
  2. Drive vehicle over a known measured distance. If odometer is reading accurately, go to next step. If odometer is inaccurate, go to step 4).
  3. Drive vehicle at a steady speed over a known distance and record travel time. If speedometer meets calibration tolerances, system is okay. See SPEEDOMETER CALIBRATION TOLERANCE  table. If speedometer does not meet calibration tolerances, replace speedometer. See SPEEDOMETER/ODOMETER  under REMOVAL & INSTALLATION.
    SPEEDOMETER CALIBRATION TOLERANCE (1)

    Actual Speed MPH (KM/H) Allowable Range MPH (KM/H)
    30 (48) 28-35 (45-56)
    60 (97) 58-65 (93-104)
    (1) Odometer tolerance: 9.6-10.3 miles (15.4-16.6 km) over a measured 10 miles (16 km).
  4. Check for correct drive and driven gear on speed sensor. See Fig 1 . If drive and driven gears are correct as specified, go to next step. If gears are incorrect, install correct drive and driven gears and retest system.
  5. Raise drive wheels off ground and support vehicle. Disconnect Vehicle Speed Sensor (VSS) connector. Connect an A/C voltmeter between output terminals on A/T mounted VSS. Operate vehicle in drive. If voltage is 1.3-6.1 volts AC, go to step 8). If voltage is not 1.3-6.1 volts AC, go to next step.
  6. Remove VSS from A/T. Verify presence of speedometer gear with all teeth in good condition and presence of retainer clip. If driven gear teeth are okay and clip is present, go to next step. If gear teeth are not okay and/or clip is not present, replace gear and clip and retest system. See Fig 1 .
    Fig 1: Speedometer Drive/Driven Gear Usage
    G96J01240Courtesy of FORD MOTOR CO.
  7. Verify presence of speedometer drive gear on output shaft. If drive gear is present, replace VSS and retest system. If drive gear is absent, repair transmission as necessary and retest system.
  8. Turn ignition switch to OFF position. Remove instrument cluster. See INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. Measure resistance from ground to cluster connector C251, terminal No. 16 (Gray/Black wire). See Figure . If resistance is 5 ohms or less, repair short in Gray/Black wire and retest system. If resistance is more than 5 ohms, leave ohmmeter connected to Gray/Black wire and go to next step.
  9. Connect jumper wire between ground and VSS connector Gray/Black wire. Measure resistance from Gray/Black wire at VSS connector to ground. If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, repair open Gray/Black wire and retest system.
  10. Disconnect VSS connector. Measure resistance from ground to Pink/Orange wire at VSS connector. If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, repair open Pink/Orange wire and retest system.
  11. Measure resistance between VSS terminals. If resistance is 175-400 ohms, go to next step. If resistance is not as specified, replace VSS and retest system.
  12. Measure resistance between ground and cluster connector C251, terminal No. 14 (Pink/Orange wire). See Figure . If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, repair open Pink/Orange wire and retest system.
  13. Disconnect cluster connectors. Check continuity from speedometer contact clips to printed circuit. If continuity is present at all clips, go to next step. If continuity is not present at all clips, replace contact clips and retest system.
  14. Reconnect cluster connectors. Check continuity of printed circuit from speedometer contact clips to cluster connector using speedometer continuity table as a guide. See SPEEDOMETER CONTINUITY  table. If there is continuity at all circuits, replace speedometer and retest system. See SPEEDOMETER/ODOMETER  under REMOVAL & INSTALLATION. If continuity is not present at all circuits, replace printed circuit and retest system. See PRINTED CIRCUIT  under REMOVAL & INSTALLATION.
SPEEDOMETER CONTINUITY

Connector - Pin No. (Wire Color) Function
C251 - 3 (RED/YEL) Power Input
C251 - 12 (LT BLU/PNK) Power Input
C251 - 14 (PNK/ORG) Ground
C251 - 16 (GRY/BLK) VSS Input
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