Test G: Speedometer/Odometer Inaccurate (SHO)

NOTE: Instrument cluster (speedometer) receives an input from ABS module 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. Using NGS tester, monitor Semi-Active Ride Control (SARC) PID VSS_SRC. 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 open in Gray/Black wire.
5. Measure resistance between ground and terminal No. 12 (Gray/Black wire) at ABS control module harness connector C1057. See Fig 1 . If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, repair open in Gray/Black wire.
6. Measure resistance between ground and terminal No. 8 (Gray/Black wire) at instrument cluster harness connector C250. See Figure . If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, repair open in Gray/Black wire.
7. 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, replace contact clips.
8. Reconnect 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
   
   

   Connector-Terminal No.	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

Fig 1: Identifying ABS Control Module Harness Connector C1057 Terminals

Courtesy of FORD MOTOR CO.