I have a 2012 GL 450 that has a 2004 code, looking at all the videos it looks like you need to pull the manifold to repair. What is the worse that can happen if I just leave it alone?

 

the worst that could happen is that your check engine light stays on.

this happens to almost all m273 motors due to hardening of the plastic pushrod link that operates the tumble flaps - they just snap off with age.

it doesn’t need fixed really, you can if you want rotate the tumble flap pivot arm to its extreme counterclockwise position to avoid triggering the CEL.

i have two of these; both have the issue and I’ve noticed no difference in fuel economy or drive ability.
tgat being said, I have repair kit made by Üro and will try this repair - the manifold does have to come out and is a quite lengthy and laborious repair.

 

I clear is an it comes back after a while. I guess I will leave it alone unless I get to feeling real energetic and borb.
Thanks