Check engine code P0611?

This code came on a year ago and although I didn’t notice any issue I took it to Mercedes they said they fixed it and gave me a huge bill, a few months later the same light came back on so I took it to a trustable Volvo mechanic he told me he couldn’t find the issue so he only charged me a flat rate and he cleared the code, from that day in 2022 the code never came back on and I never had an issue until earlier this year. My car stalled in Feb of this year, but no lights came on. I just lost power and then it worked normally after that. Just two weeks ago is when the code showed back up and the only difference, I’ve noticed in the car is a louder humming noise but that could’ve been from the vents because it’s hotter in my area now than it has been so could be completely unrelated. Just need some help diagnosing because I can’t afford to take it back to Mercedes.