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Speedometer/Odometer Inaccurate (Except 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 SPEEDOMETER CALIBRATION TOLERANCE  table. If speedometer fails to meet speedometer calibration tolerance, replace speedometer assembly.
    SPEEDOMETER CALIBRATION TOLERANCE (1)

    Actual Speed-MPH Allowable Range-MPH
    30 27.7-34.5
    60 57.4-64.1
    (1) Odometer measured over actual 10 miles: 9.6-10.3 miles.
  4. Check for correct driven gear on speed sensor. If driven or drive gear is suspect, refer to manufacturer's parts department for correct specifications in relation to final drive ratio and tire size. If parts are correct, go to next step. If parts are not correct, install correct parts and retest system.
  5. Partially remove instrument cluster. See INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. Disconnect instrument cluster connectors C250 and C251. Measure resistance between cluster connector C251, pin No. 16, (Gray/Black wire) and cluster connector C250, pin No. 8, (Black/Yellow wire, Brown wire on flex fuel vehicles). If resistance is 200-300 ohms, go to step 8). If resistance is other than 200-300 ohms, go to next step.
  6. Disconnect VSS connector. Measure resistance across terminals of VSS. If resistance is 200-300 ohms, go to next step. If resistance is other than 200-300 ohms, replace VSS and retest system.
  7. Measure resistance between cluster connector C251, pin No. 16, circuit No. 679 (Gray/Black wire) and ground. If resistance is 10 k/ohms or less, repair short to ground in circuit No. 679 (Gray/Black wire) and retest. If resistance is more than 10 k/ohms, leave ohmmeter connected and proceed to next step.
  8. Using a jumper wire connected to ground, connect other end to circuit No. 679 (Gray/Black wire) at VSS connector. Observe ohmmeter still connected from previous step. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair open in circuit No. 679 (Gray/Black wire) and retest system.
  9. Disconnect ohmmeter and jumper wire from circuit No. 679 (Gray/Black wire). Connect ohmmeter to cluster connector C251, pin No. 13, (Black/Yellow wire, Brown wire on flex fuel vehicles). Measure resistance to ground. If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, repair open in Black/Yellow wire (Brown wire on flex fuel vehicles), and retest system.
  10. 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.
  11. Reconnect cluster connectors. Check continuity from speedometer contact clips to cluster connector pins. See PRINTED CIRCUIT CHECK table.
    PRINTED CIRCUIT CHECK

    Cluster Connector Circuit No. (Wire Color) Function
    C251-6 1003 (GRY/YEL) Power Input (RUN)
    C250-5 729 (RED/WHT) Power Input (Battery)
    C251-13 (1) GROUND
    C251-16 679 (GRY/BLK) VSS Input Signal
    (1) Circuit No. 398 (Black/Yellow wire) on models without flex fuel. Circuit No. 564 (Brown wire) on models with flex fuel.
  12. If there is continuity in all circuits, replace speedometer assembly and retest system. See SPEEDOMETER/ODOMETER  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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