A bad output sensor, or an electrical disconnect at it, will activate "limp mode". Speedometer won't work either as
sideburns2009 says. I know because I disconnected my 2002's once and found that out. CEL will normally come on with "limp mode".
Check for stretched / broken wires, caused by unsecured weight of the bulky wiring harness pulling on them, at the output sensor. Recently
Miron had a problem with a broken wire to the output sensor per this
Post.
As to a quick learn, it's not normally required any more than for a transmission fluid change. The "intelligent" transmission will adjust on its own the same as it does to a transmission fluid change. When discussing this with some mechanics at a local Chrysler Dealership, a couple years back, they said that a "quick learn" was not normally required with a solenoid pack change.
Like with a transmission fluid change, a "quick learn", which puts the transmission shifting settings back to "default" settings, may/will help the transmission adjust quicker and be smoother. My last fluid change, without "quick learn", took about two weeks to get things back to normal. They say 75 restarts/operation max. should do it.
What activates "limp mode"? This
Post has some info on that.