Ok, don't worry about the bcm, it only receives a message from the liftgate ajar switches, so it will know if the liftgate is open or closed, it wont alter the wiper operation. however if you had a high end scan tool you could check the ajar switches which supply the ground for the rear wiper.
basically if the power check ok, then it would be a ground problem.
lets back a bit and make sure the easy is ok, there are two fuses for the rear wiper, there is a 25 amp fuse in the under hood fuse blocked marked RR WPR make sure this fuse is good. the second fuse is in the ip fuse block on the left side of dash, this fuse is a 15 amp blue fused also marked RR WPR. if both these fuses are good, then we can make the voltage checks at the wiper motor.
here is a brief description on the system works.
The rear wiper/washer system consists of the following components:
|• ||Rear wiper/washer switch|
|• ||Window wiper module-rear|
|• ||Window washer pump-rear|
Rear Wiper/Washer System Operation
The rear wiper module controls rear wiper motor operation. Battery voltage supplied to the module is used to operate the wiper motor in all modes and to return the rear wiper arm to the park position after the ignition is turned off. Accessory voltage supplied to the rear wiper/washer switch is used to supply the rear window wiper and washer switch signal circuits. In wiper switch positions 1 and 2 the wiper switch signal circuit voltage level to the wiper motor module determines the wiper motor delay interval. The rear window washer pump supply voltage circuit is used to provide the operating voltage for the rear washer pump for as long as the rear washer switch is pressed. The rear window washer switch signal circuit is used as a wash signal to the rear wiper motor module to operate the wipers during the rear wash operation.
The liftgate ajar switch signal circuit provides information to the rear window wiper module about the status of the liftgate. If the liftgate or liftglass is open the rear wiper operation is not performed.