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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3567
Experience:  Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes
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2012 ML350 Bluetec RPM will not exceed 1200. Coded P0234

Customer Question

2012 ML350 Bluetec RPM will not exceed 1200. Coded P0234 (overboost) & P0471 (exhaust pressure)
Submitted: 1 year ago.
Category: Mercedes
Expert:  JACUSTOMER-n3f1w267- replied 1 year ago.

Hi my name is ***** ***** I'll try my best to help you! What's the millage on the car?

Customer: replied 1 year ago.
2012
Customer: replied 1 year ago.
I should add that we restarted a couple of times and it seemed to reset and perform fine. After some shutdowns no change.
Expert:  JACUSTOMER-n3f1w267- replied 1 year ago.

The exhaust sensor itself could be the problem , can you read the value of the sensor with a scan tool ?

Customer: replied 1 year ago.
Have both parts on order. will replace exhaust sensor and both boost sensors. let you know if need to go further. I can read ohms on the exhaust sensor...if need be
Expert:  JACUSTOMER-n3f1w267- replied 1 year ago.

perfect ! change parts and clear faults . Cycle the key and wait 30 seconds .they can be tricky sometimes !

Expert:  JACUSTOMER-n3f1w267- replied 1 year ago.

but first change the pressure sensor first . you could save money by returning the other parts .

Customer: replied 1 year ago.
Replaced boost sensor and exhaust sensor...essentially same problem. Disconnected battery to reset..no go. Engine wont rev above 1300 when leaving 3rd gear. Shut down engine and engaging paddles and can turn 4,000 as soon as speed gets past 3rd gear, rpm drops. Codes are now P0402, P0234 7 P006D.
Customer: replied 1 year ago.
Also observed no "O" ring in the intake tube to the turbo... I mean gone. installed new o ring and replaced gaskets on mass airflow housing.
Customer: replied 1 year ago.
oh, mileage 55,000
Expert:  JACUSTOMER-n3f1w267- replied 1 year ago.

The orange o-ring is not in place !?

Expert:  JACUSTOMER-n3f1w267- replied 1 year ago.

after you changed the o-ring , no change !?

Customer: replied 1 year ago.
no change.
Expert:  JACUSTOMER-n3f1w267- replied 1 year ago.

Ummm , we have a really strange problem .... Can you provide me a picture of the pressure sensor ? The engine goes in over boost to protect itself and shut the turbo down . So once we get the pressure sensor to work correctly it will boost as normal ... If you remove the inlet tube from the turbo , can you turn the turbo with your finger ? Can you provide me a picture of the sensors you have change? We will make it work don't worry but those engines are pretty complicated and there's a lot of pieces who works together , so we need to go by elimination !

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