Check engine light keeps coming on- Volvo XC60 - 2012

What is your question?

Check engine light comes ... I go right to the dealer and computer error points to the #6 cylinder injector which I replace. All good - 2 weeks later the same issue. Dealer replaces #5 injector. A few weeks later the same issue - Dealer has NO idea whats happening and the error keeps pointing to the #6 cylinder injector. Car runs great otherwise and when it starts up rough in the morning - or gradually starts get rougher over a few mornings I know its gonna happen again... I really dont want to keep replacing these injectors (4 to go) as its expensive unless for sure I know that's the issue... Would you have any thoughts? I have 135k miles - all highway driving as I put on about 100 highway miles a day. As I said car seems to run great otherwise.

What makes this problem better or worse?

Car actually runs fine but I dont like having a check engine light on

How long has your 2010 Volvo XC60 had this problem?

on and off for 6 months now