Cadillac: 1996 El Dorado Speed Sensor Fault, cadillac el dorado, output shaft

Question
My mother-in-law's 1996 Cadillac El Dorado is giving her a Speed Sensor Fault, Is this something serious?  I am pretty good with engines, and electrical systems, but cadillacs are a mystery to me...is this sensor something I can change? If so, where is it?

Answer
What is the code ?. It could be an internal speed sensor inside the trans or the external sensor for the speedometer. If what your looking for is the speedometer sensor it is located on top of the trans near the output shaft at the passengers side of the engine and has 2 electrical wires attached to it.