Test F: Speedometer/Odometer Inaccurate (Except SHO)

NOTE: Instrument cluster (speedometer) receives an input from the vehicle speed sensor to determine vehicle speed.

1. Connect NGS tester to Data Link Connector (DLC). Using NGS tester, monitor PCM PID VSS (+). Road test vehicle and monitor PID VSS (+). If the speedometer is operating and vehicle speed signal exists, go to next step. If speedometer is not operating and/or no vehicle speed signal exists, 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 fails to meet speedometer calibration tolerance, go to next step. See SPEEDOMETER CALIBRATION TOLERANCE  table. If speedometer meets speedometer calibration tolerance specifications, system is okay at this time.
   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 vehicle 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.
5. Disconnect instrument cluster harness connector C250. Measure voltage at terminal No. 5 (Red/White wire) at instrument cluster harness connector C250. See Figure . If battery voltage exists, go to next step. If battery voltage does not exist, repair power distribution circuit as necessary. See appropriate wiring diagram in POWER DISTRIBUTION article in WIRING DIAGRAMS.
6. Disconnect instrument cluster harness connector C251. Measure voltage at terminal No. 6 (Gray/Yellow wire) at instrument cluster harness connector C251. See Fig 1 . If battery voltage exists, go to next step. If battery voltage does not exist, repair power distribution circuit as necessary. See appropriate wiring diagram in POWER DISTRIBUTION article in WIRING DIAGRAMS.
7. Measure resistance between ground and terminal No. 13 (Black/Yellow wire, Brown wire on flex fuel vehicles) at instrument cluster harness connector C251. If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, repair open in ground circuit. See appropriate wiring diagram in GROUND DISTRIBUTION article in WIRING DIAGRAMS.
8. Measure resistance between terminal No. 16 (Gray/Black wire) and No. 13 (Black/Yellow wire, Brown wire on flex fuel vehicles) at instrument panel harness connector C251. If resistance is not 200-300 ohms, go to next step. If resistance is 200-300 ohms, disconnect Vehicle Speed Sensor (VSS) harness connector C1043 and go to step  10 .
9. Disconnect Vehicle Speed Sensor (VSS) harness connector C1043. Measure resistance between terminals at VSS (component side). If resistance is 200-300 ohms, go to next step. If resistance is not 200-300 ohms, replace VSS.
10. Measure resistance between ground and terminal No. 16 (Gray/Black wire) at cluster harness connector C251. If resistance is greater than 10 k/ohms, leave ohmmeter connected and go to next step. If resistance is 10 k/ohms or less, repair short to ground in Gray/Black wire.
11. Using a jumper wire connected to ground, connect other end to Gray/Black wire terminal at VSS harness connector C1043. If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, repair open in Gray/Black wire.
12. Disconnect instrument cluster harness 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 at any clip, replace contact clips.
13. Connect instrument cluster harness connectors. Check continuity from speedometer contact clips to cluster harness connector terminals. See PRINTED CIRCUIT CHECK  table. If there is continuity in all circuits, replace speedometer assembly. If continuity is not present in all circuits, replace instrument cluster printed circuit.
    PRINTED CIRCUIT CHECK
    
    

    Connect-Terminal No.	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.

Fig 1: Identifying Instrument Cluster Harness Connector C251 Terminals

Courtesy of FORD MOTOR CO.