This is mounted on the B post and the loop moves SIDEWAYS to pull the door in at the back. This is the first/last movement when the door opens/closes.
The actuator can also be adjusted a small distance sideways to reduce the pressures on the door lock.
To see if the actuator needs adjusting, close the door and check the door is flush with the body. The two Torx bolts can be slackened to allow the actuator mechanism to move a little in and out. A slight smear of grease on the actuator loop will aid initial disengagement of the latch.
On mine, the driver's B-post actuator was starting to get a bit wheezy - so rather than fit a new actuator right away, I squirted a little synthetic grease into it. Inspection of my spare actuator shows that it is mounted so the motor and gearing are BELOW the two mounting screw holes. Part #'s are: Driver's (right): 9164.65 and Passenger (left): 9164.66
So - by removing the lower T40 Torx screw, I could spray in a little synthetic grease - which hopefully would drop down into the moving bits.
In practice it seems to have done exactly that, and it lasted another 7 years until it slowed again - so I replaced it as below.
Open the door.
After switching off the ignition, wait 3 minutes before disconnecting the battery.
When the door is closing, the last action is to pull in the door at the rear. The locking unit (hook in the B-post) pulls in the door and sends a signal to the control unit: "door is closed".
In this unit, in addition to a small electric motor, there are a pair of micro-switches which are operated by cams on an internal shaft.
With the help of a plastic or wooden wedge the plastic cover at the bottom of the door opening can be clipped out.
Sometimes the white blocks stay behind but they easily can be removed with a flat screwdriver and put back in the cover.
Next remove 2 x Torx (T40) screws (items 2 on the drawing above) holding the actuator from the B post.
Take care, the unit is still fixed with a hook to the body of the car.
Using your hand from underneath you can unclip the fixing on the bottom of the unit (3 in the drawing above) and then the unit can be taken out.
Reassemble and finally adjust the two torx screws so the door is flush with the bodywork when closed.
When finally replacing the cover, note that the hard plastic of the cover fits OVER the rubber seal (you might expect it to fit under - but it doesn't).
In the B-post actuator there are some contacts which gives the exact position of the actuator. They can sometimes fail.
Mystery when the B-post actuator seems to work in reverse: it has been found that the actuator can push OUT when the door is closing but pull IN when the door should be opening.
The B-post actuator should send a signal to the ECU when it is fully pushed out or fully pulled in; if these signals are lost then the ECU won't know what to do - so it could be a faulty connection anywhere - or just temporarily confused electronics! Sometimes a new actuator is fitted and works fine, but still can't be certain that was where the fault was.