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Car playing up today agin with boost (or lack of).

Had it scanned and the fault says 'Charge Pressure Maximum Limit Exceeded P1555 Upper limit reached - Intermittent'

I have a post further down where someone mentioned the brake switch but that seems fine.

Anyone had the above and what was the cure? I'm thinking N75 valve which has never been replaced but could it be anything else?

MM

N75 was the culprit when I was getting that code. The valve had not completely failed, but was slow to react, so under hard acceleration in a higher gear, it would throw the code and go into limp mode.

Other possibility is a leak in one of the various lines to/from the turbos. Replacing the N75 valve is the easiest, but most expensive test. You can also disconnect the wastegate line from the N75 and put pressure to it to make sure it holds the pressure, and the wastegates are opening. If so, then it's back to replacing the N75.

Good luck!

Is there just one valve or one for each turbo?

Just one.

Could be pressure sensor but my money's on the N75.

Yeah, and unlike pretty much everything else on these cars, it's pretty easy to get to. Just remove the air cleaner assembly and it's hanging off the back of the intake manifold.