2017 GLS550 Turbo A Underboost CEL

[rpaoness]

In a surprising turn of events, the CEL shut off on it's own during a few normal driving cycles. Must be intermittent enough to repeatedly meet parameters.

[rpaoness]

And as expected it came back. Coincidentally I now have an occasional startup rattle on the GLA45 that's probably the same thing.

[kevm14]

You would start with checking the vacuum check valve and associated lines and controls...and wait until it's actually a problem. Though that turbo is waaaaay more accessible.