So after a 10hr round trip on weekend my 05 GC 5.7 Limited threw engine light..when I did the key dance it showed up p0521 and p0406..my understanding is thats egr and oil weight issue is that correct? Car is running like a dream no issues at all..seems strange .
Looked at service book and the prev services by dealer for past owner have been with 10w40 oil apparently..ill change that out myself to the 5w20.
Do these two show up together for particular reason? Only sign I noticed was at low speed driving thru a town looking for a certain street I noticed a fluttery sound from exhaust when just cruising at slow speed..I thought maybe that was an mds issue due to heavier oil?
Open to suggestions!