Ford Repair: 2000 Ranger PCM, 3.0 Auto, 40K, vehicle speed sensors, sensor circuits

Question
Yesterday my ranger had three strange things happen at once.  The speedometer quit working, the ABS light came on, and the shifting was very erratic.  The speedo will come on at about 40mph.  The first shift (very hard) causes the OD light to flash.  Previously the check engine light has come on and the code indicates O2 sensor which I changed with no result.  Idle and mpg has never been good.  Is my PCM bad?  Is the ABS light, speedo, and shifting related?  Help me Dave.  Dazed and Confused in Honolulu, Leslie

Answer
The Speedometer, ABS, and Transmission all rely on the Vehicle Speed Sensors.  I would guess that if these systems all started acting up at the same time, one of the speed sensors went bad.  As for the Check Engine Light, it comes on when the PCM finds one of the emissions sensor circuits to be out of their normal range.  The system would have to be scanned to retrieve any Diagnostic Trouble Codes, and you would have to determine why the specified circuit went out of range.  It could be a bad sensor, wiring problem, or just a symptom of a different problem.  I don't think that the PCM is bad.

I hope this clears things up a little.
Dave