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Speedometer/Odometer Inaccurate (SHO)

WARNING: This page is about a different car, the 1997 Mercury Sable and 1997 Ford Taurus. However, it is still accessible from the selected car via links, so may be relevant.
  1. Road test vehicle. If the 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 inaccurate, go to step 4).
  3. Drive vehicle at a steady speed over a known measured distance and record time taken to travel that distance. If speedometer meets speedometer calibration tolerance specifications, system is okay. See the SPEEDOMETER CALIBRATION TOLERANCE  table. If speedometer fails to meet speedometer calibration tolerance, replace speedometer assembly.
  4. Connect New Generation Star (NGS) tester to data link connector below instrument panel. Access SARC PID. Select VSS_SRC from PID menu. Monitor vehicle speed on tester, while test driving vehicle. If vehicle speed shown on tester is approximate vehicle speed, go to next step. If vehicle speed shown on tester is not approximate vehicle speed, repair circuit No. 679 (Gray/Black wire).
  5. With an ohmmeter connected to ground, measure resistance of circuit No. 679 (Gray/Black wire) at ABS control module connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair circuit No. 679 (Gray/Black wire) for open circuit and retest system.
  6. With an ohmmeter connected to ground, measure resistance of circuit No. 398 (Black/Yellow wire) at instrument cluster connector C250. If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, repair circuit No. 398 (Black/Yellow wire) for open circuit and retest system.
  7. Disconnect cluster connectors C250 and C251. With an ohmmeter check speedometer for continuity from contact clips to printed circuit. If there is continuity at all clips, go to next step. If there is no continuity, replace contact clips and retest system.
  8. Reconnect cluster connectors. Check continuity from speedometer contact clips to cluster connector pins. See the PRINTED CIRCUIT CHECK  table.
    PRINTED CIRCUIT CHECK

    Connector Circuit No. (Wire Color) Function
    C251-10 1044 (WHT/YEL) Power Input (RUN)
    C250-1 57 (BLK) GROUND
    C251-16 679 (GRY/BLK) VSS Input Signal
  9. If there is continuity in all circuits, replace speedometer assembly and retest system. See SPEEDOMETER  under REMOVAL & INSTALLATION. If continuity is not present in all circuits, replace instrument cluster printed circuit and retest system. See PRINTED CIRCUIT  under REMOVAL & INSTALLATION.
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