The wiper arm on my rear window is broken. How

OK, there's at least a fuse problem to be investigated. If the rears stopped first, then look at the harness that runs thru a rubber tube from the roof line into the rear hatch. These wires can break with age. It's rather fiddly to fix, but can be done.

If the fronts got slow then stopped, pull the valence panel in front of the windscreen and then the wiper arm assembly. The arm pivots often rust up with age, effectively overloading the motor. It's fixable, but the replacement arm assembly is not unreasonably expensive.
Wiper motors rarely burn out, but is not impossible.

guessing sucks, no? very expensive..!!! what year CAR?
ever heard of a $20 DMM that all have a voltmeter?
yes, use a volt meter.
if you had , you would have found that there was no
power to the motor, when activated.
the motors on all wipers are self sustaning of zero point.
that means that it self powers up inside with its one power switch.
so some need power on 2 pins, RTM read the FSM its there .
ever wonder why wipers keep going when turn off, that is it returns for FREE. bingo on self power I(no this is not free energy , lol)

there are only 2 pissible.
1: no power.
2:its jammed, same is true for all Elect motors, be it wiper , windows, fans, sure anything.

rear windows are pretty much not jammable but ive
never look inside the rear rear door of the not stated year, Subaru.
but if you look and see arms in there, bingo. they are jammed
one way to do this , done many a time.
is to release just the motor arm and then cycle the mechanism
by hand, oops , jammed.

no power, or jammed.

They're held on typically in one of 2 ways. One type has a tapered shaft and a nut that holds the arm down. There may be a cap over the nut that would need to be removed first.The other type, more typical for American cars, has a straight, splined shaft. To remove these, you would lift the wiper arm, then there is a small tab on the side of the arm that you pry sideways away from the arm that will hold the spring tension when you let the arm back down, then you can wiggle the arm straight up and off the shaft.

Hi,
Yes, the wiper is a two piece wiper. Can not be bought at Walmart.
One piece is bolted to the Jeep. The other section has the wiper attachted.
You have to get this at the Jeep dealer or on line. The complete wiper assembly is about $38.00 or $17.00 for the wiper, with the broken tip.
I have a 2006 Grand Cherokee and that happen to me also.
Jeff

check your fuses

replace wiper arm..it has a spring in it to push it to the window

Inspect the wiper where it attaches to the motor for any broken or missing parts. Also, examine the wiper itself for damage. If so replace it with another from your local auto parts store. Also if you ask, they will install it for you.

Men will always protect/support the other men so I will check my wording :-))

First check the condition of the wiper shaft outter splines when the wiper arm is removed (emerging from the wiper grill) Clean any corrosion and dirties. If the spine is worned or in bad condition then the wiper pivot will have to be replaced by a new one (few nuts to be unscrew by under the wiper grill and disconnecting from the link kit rods). Eventhough the splines seem to be ok, turn ignition switch and wiper switch on and check if the pivot shaft is moving back and forth. If not, there is a problem with the link kit rod disconnected in a joint.

If the shaft splines are ok and shaft is moving then check the wiper arm inner splines. Chances are that they are in bad condition (the arm metal being 'softer' than the pivot spline metal. If it's the case, have the arm replaced.
Replacing any parts make sur outter and inner splines are well engaged/fitting before tightening arm bolt
Sorry for my english
Hope it will help
Dan

put oil on the pin that fastens the arm to the rotator. work the arm up and down several times to work out the grindge and rust. Reoil and repeat several times
wiper will rest on the window for full operation

the linkage has popped off the back you need to get to it to push it back on ots possibly worn and needs replacing