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Speedometer/Odometer Reads Inaccurately

WARNING: This page is about a different car, the 1997 Mercury Cougar and 1997 Ford Thunderbird. However, it is still accessible from the selected car via links, so may be relevant.
  1. Road test vehicle. If speedometer is operating properly, go to next step. If speedometer is not functioning properly, go to step 5).
  2. Drive vehicle over a known distance. If odometer reads accurately, go to next step. If odometer does not read accurately, go to step 4).
  3. Drive vehicle at steady speed over known distance and record time taken to travel distance. See SPEEDOMETER CALIBRATION  table. Allowable range for odometer over measured 10 mile distance is 9.6-10.3 miles. If speedometer meets calibration specifications, system is functioning properly. If speedometer does not meet calibration tolerance specifications, replace speedometer assembly. See SPEEDOMETER/ODOMETER  under REMOVAL & INSTALLATION.
    SPEEDOMETER CALIBRATION

    Indicated Speed (MPH) Allowable Range (MPH)
    30 28-34
    60 58-65
  4. Remove Vehicle Speed Sensor (VSS). Verify presence of driven gear (with all teeth in good condition) and retainer clip. If teeth are okay and clip is present, go to next step. If teeth are damaged or clip is absent, replace with proper gear and/or clip and retest system.
  5. Remove instrument cluster. See INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. Disconnect cluster connectors C250 and C251. See Figure and Figure. Measure resistance between cluster connector C250, pin No. 1 (Gray/Black wire) and cluster connector C251, pin No. 6 (Red/Yellow wire). If resistance is 200-300 ohms, go to step 8). If resistance is not 200-300 ohms, go to next step.
  6. Disconnect VSS connector. Measure resistance between VSS terminals. If resistance is 200-300 ohms, go to next step. If resistance is not 200-300 ohms, replace VSS and retest system.
  7. Ensure ignition is off. Measure resistance between ground and cluster connector C250, pin No. 1 (Gray/Black wire). If resistance is 10 k/ohms or less, repair short to ground on Gray/Black wire and retest system. If resistance is more than 10 k/ohms, go to next step.
  8. Install jumper wire between ground and VSS harness connector Gray/Black wire. Measure resistance between ground and cluster connector C250, pin No. 1 (Gray/Black wire). If resistance is 175-400 ohms, go to next step. If resistance is not 175-400 ohms, repair open in Gray/Black wire and retest system.
  9. Measure resistance between ground and VSS connector Pink/Orange wire. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair open on Pink/Orange wire and retest system.
  10. Connect cluster connectors C250 and C251. Measure resistance of instrument cluster printed circuit between indicaed terminals of printed circuit flex connection and terminals of gauge. See the SPEEDOMETER CIRCUIT CHECK  table. If resistance is less than 5 ohms for each circuit, replace speedometer and retest system. Refer to SPEEDOMETER/ODOMETER  under REMOVAL & INSTALLATION. If resistance is more than 5 ohms, replace printed circuit. See PRINTED CIRCUIT  under REMOVAL & INSTALLATION.
SPEEDOMETER CIRCUIT CHECK

Cluster Connector: Pin No. (Wire Color) Gauge Terminal
C251-6 (RED/YEL) B +
C250-3 (GRY/RED) GND
C250-1 (GRY/BLK) SIG
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