Hello! I have tried solving this issue on my own by reading through all the forum posts from multiple different websites, but all of these seem to be slightly different from my current issue. I have seen some pushback from this question on other forums, but I promise this one is actually different!

Anyways, my 2012 m37x has had what seems to be the dreaded codes (P0021, P0524) along with P0456. When I initially got the code, I went straight to the mechanic and they diagnosed the issue as a bad vvt solenoid. Interesting to note that the car was NOT in limp mode when the codes first appeared. I replaced the vvt solenoids and then the car drove fine for about 150km. However, after a long drive the codes came back and the car was in limp mode. Naturally I took the car back to the mechanic. He said he wasn’t sure what the issue is, and that I needed to take it to an electrical mechanic (?). I would assume that he had tested the oil pressure and other tests to rule out a mechanical issue.

As for any symptoms, when I clear the codes, the car will drive anywhere from 15km-100km without the codes coming back (driving on highways seems to increase the range). I also notice on cold startups there is a gassy smell and I think the car is running a bit rich (fuel milage is slightly impacted. The code will also never show up on a cold startups, only after the engine is warmed up. Please let me know if this is something that absolutely needs to be brought in, or if there are some things that I can try at home. Thanks for any help!

 

Hey, how many Miles have the engine ? You gallery gasket is ok because oil pressure is good but it's possible your tensioner was used by miles ;
For the P0456 it's possible just because you have the P0021 and P0524, or you can read this : https://static.nhtsa.gov/odi/tsbs/20...53007-9999.pdf
It's possible with multichanel oscilo see syncro of cameshaft withouth remove engine .