Volvo VNL 670 year 2017 CAC issues

hello, i got volvo semi tractor, VNL 670, year 2017. Back in december gave it to mechanic because of engine derate issue. they changed fuel water separator and changed CAC pipe. within two months, engine light came up again, and engine derated, mechanic now suggesting to replace CAC. would need advice, whats going on with engine? is there any relation of CAC replacement with CAC pipe or its just normal wear tear? market is crazy and seems im paying mechanic $4-5 grnads every second month.

 

yes, back in december, 2022 they pressure tested and found CAC pipe leaking, they replaced it. now because of engine light, they found code and with pressure testing they are replacing CAC now. both jobs costing me $7000 and $ 3000 respectively. in earlier job they did replaced fuel water separator as well