Q: I am trying to figure out a problem with a 4WD 2000 Ford F-150 V-8. The speedometer reads correctly up to about 45 mph, but then it gets stuck there no matter how fast you go. The cruise control works correctly at all speeds.

A: In this 2000 model system, mph information begins with the Vehicle Speed Sensor mounted at the transmission's output shaft. The PCM receives this VSS input, translates it, and shares the data with other modules -- including cruise control and the instrument cluster (speedo-meter). So your short description of the problem actually tells us quite a lot. We know the VSS is working, or you would have mentioned the malfunction indicator lamp coming on. We also know the PCM is receiving the speed data, and transmitting the information to both the cruise control module (servo) and the instrument cluster. The cruise works fine, and the speedo works halfway. Barring any off-the-wall short in the system, the problem is more than likely an internal fault within the instrument cluster. The speedometer itself is non-serviceable.

The fix will require instrument cluster replacement or repair. Your local Ford service department should sublet to an electrical repair shop. If you have the time, a full confirmation of the failure can be obtained by observing the odometer display. Check the speed at which the tenths of a mile pass by while driving at about 40 mph, then speed up considerably to highway speeds. The tenths should now be passing by more quickly. This confirms that the instrument cluster is receiving the correct speed data, and the hangup is the speedometer itself. One note: There were some software issues with your truck when replacing the PCM or the instrument cluster, which requires an update to fix.


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