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The parking brake actuator is built into the rear brake calipers.
Did the caliper piston compress easily?
When you compressed the piston back into the caliper, you need to turn the piston at the same time push it into the caliper. Is this how you got the pistion to compress?
If you look closely at the rear brake pads did you notice the metal tab on the metal backing of the brake pad?
This metal tab aligns with one of the notches that are on the caliper piston. If you did not get the metal tab on the back of the brake pad lined up with the caliper piston notch, the parking brake will not work.
I recommend removing the rear calipers and checking this.
If the rear pads are not installed correctly into the caliper piston notch then the parking brake will not work. Before you install the caliper with the pads in the bracket, you will need to ensure the notches are in the correct position. They are usually set vertical to the caliper. This is kind of hard to explain but when you take the caliper back apart you will notice what i am talking about. There is 4 notches on the piston and one of the notches will need to be lined up with the pin on the back of the brake pad.
Also there is a adjustment for the rear ebrake under the center console cover.
If you have any other questions please let me know.