Recently my check engine light came on and since all modern day vehicles have computers I had a diagnostic check run on my truck. It’s a '97 Dodge 1500 with a V8, automatic. The test said I had a malfunction with the output speed censor. WTF is it for, what does it do, and where is it located on the vehicle so I can change it out.
I sure do miss the days when you listened to your motor and you could diagnose your problem.
So, any info would be great.
That should be the same as a vehicle speed sensor, in which case it produces a speed signal for the ECU (computer) and the speedometer. It’s located on the side of the transmission case, where the speedometer driven gear was installed in previous designs.
Speed sensor failures are fairly common, but be aware that the same code can be set by a faulty speedometer drive gear, wiring problems in the sensor circuit, etc.
Gary T. probably has it right about the speed sensor.
But the “output speed censor” that you mention would be that highway patrolman hiding behind the billboard with his radar gun. 
Don’t believe it! Modern ECUs (electronic control units) have made 100K miles between tune-ups routine!
I have heard from checking other forum posts that the 720 code is the speed sensor on the side of the tranny and the 500 code is for the rear speed sensor which is on top of the differential.
I have also heard that cleaning the sensor fixed the problem.
The sensor is magnetic and works by detecting a gear tooth passing in front of it. Since it is magnetic it can attract ferrous metal to the sensor probe tip. Also check the connections and be careful with them. Keep gathering info and asking questions…
Sounds like an easy enough repair to me.
It’s located down underneath, near the knugel valve.
On some vehicles it is located near the muffler bearing.