Hi Alexander.
I feel your pain, as i am too going through the same process, light came on did the unplug the under seat connectors, clean and plug back in no joy.
removed the connectors and joined them with some other connectors again no joy, so decided to connector wire direct, no joy, changed out the pretensioner for another one no joy.
Removed the side impact sensor changed it out still light is on.
T4 is telling me its right side.
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Even with all that info i am still chasing the problem, tomorrow is another day and hopefully i will get somewhere.
PS also check you SRS fuse behind the glove box.